Methods of preparing electrochemical cells

ABSTRACT

Methods of preparing a cathode/separator assembly for use in electrochemical cells in which a protective coating layer is coated on a temporary carrier substrate, a microporous separator layer is then coated on the protective coating layer, and a cathode is then coated or laminated on the separator layer, prior to removing the temporary carrier substrate from the protective coating layer. Also, methods of preparing electrochemical cells utilizing cathode/separator assemblies prepared by such methods, and cathode/separator assemblies and electrochemical cells prepared by such methods.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of International ApplicationPCT/US00/32233, filed on 21 Nov. 2000, which claims priority to U.S.Provisional Application Nos. 60/167,150 and 60/167,149, both of whichwere filed 23 Nov. 1999.

TECHNICAL FIELD

The present invention relates generally to the fields of electrochemicalcells and of separators for use in electrochemical cells. Moreparticularly, this invention pertains to methods of preparingelectrochemical cells and subassemblies of electrochemical cellscomprising steps in which a microporous separator layer is coated on atemporary carrier substrate and a cathode active layer or an anodeactive layer is then coated overlying the separator layer, prior toremoving the temporary carrier substrate from the separator layer.Alternatively, instead of coating, the cathode or the anode may belaminated to the surface of the microporous separator layer. One or moreprotective coating layers, such as a single ion conducting layer, may beapplied on the temporary carrier substrate prior to the coating step ofthe microporous separator layer. Also, depending on whether a cathode oran anode, respectively, is combined with the separator layer, additionallayers, such as one or more protective layers, an edge insulating layer,a laminating layer, a cathode or an anode current collector layer, anelectrode insulating layer, an anode or a cathode current collectorlayer, an anode active layer such as a lithium metal layer or a cathodeactive layer; and an anode or a cathode protective layer may be appliedby coating or lamination subsequent to the coating step of themicroporous separator layer. The present invention also pertains tosubassemblies of electrochemical cells and to electrochemical cellsprepared by such methods.

BACKGROUND

Throughout this application, various publications, patents, andpublished patent applications are referred to by an identifyingcitation. The disclosures of the publications, patents, and publishedpatent applications referenced in this application are herebyincorporated by reference into the present disclosure to more fullydescribe the state of the art to which this invention pertains.

In an electrochemical cell or battery, an electrolyte element isinterposed between the cathode and the anode to prevent the flow ofelectrons from the anode to the cathode, as would occur in a shortcircuit. This electrolyte element must be electronically nonconductiveto prevent the short circuiting, but must permit the transport of ionsbetween the anode and the cathode during cell discharge, and in the caseof a rechargeable cell, also during recharge.

Typically, the electrolyte element contains a porous material, referredto as a separator since it separates or insulates the anode and thecathode from each other, and an aqueous or non-aqueous electrolyte inthe pores of the separator. The aqueous or non-aqueous electrolytetypically comprises ionic electrolyte salts and water or electrolytesolvents, and optionally, other materials or additives such as, forexample, ionically conductive polymers. A variety of materials have beenused for the porous layer or separator of the electrolyte element inelectrochemical cells. These porous separator materials includepolyolefins such as polyethylenes and polypropylenes, glass fiber andpaper filter papers, and ceramic materials. Usually these separatormaterials are supplied as porous free standing films which areinterleaved with the anodes and the cathodes in the fabrication ofelectrochemical cells. Alternatively, the porous layer can be applieddirectly to one of the electrodes, for example, as described in U.S.Pat. No. 5,194,341 to Bagley et al. and U.S. Pat. No. 5,882,721 toDelnick; and in Eur. Pat. Application Nos. 848,435 to Yamashita et al.;814,520 and 875,950, both to Delnick; and 892,449 to Bogner.

U.S. patent application Ser. No. 08/995,089 titled “Separators forElectrochemical Cells,” filed Dec. 19, 1997, to Carlson et al. of thecommon assignee, describes separators for use in electrochemical cellswhich comprise a microporous layer of a dried sol, such as a driedpseudo-boehmite sol, and electrolyte elements and cells comprising suchseparators. These dried sol or xerogel separators and methods ofpreparing such separators are described for both free standingseparators and as a separator layer coated directly onto an electrode.

When a separator layer is coated directly onto an electrode, such asonto the cathode, the porous separator coating may require a relativelysmooth, uniform surface on the cathode and also may require amechanically strong and flexible cathode layer. For example, for amicroporous pseudo-boehmite layer having a xerogel structure, smooth,strong, and flexible cathode layer properties may be required to preventcoating non-uniformities, excessive stresses, and possible cracking ofthe xerogel layer during drying of the sol coating on the cathodesurface and also during fabrication and use of electrochemical cellscontaining the xerogel-based separator. Cracking of the coated separatorlayer may lead to short circuiting of the cell.

Also, when a separator layer is coated directly onto an anode comprisinga reactive material, such as lithium metal, the composition of theapplied separator coating must be unreactive to the anode. Thus, thehydroxylic solvents, such as water and alcohols, typically used with solgel coatings, such as coatings of a pseudo-boehmite sol to form amicroporous separator layer, are too reactive for direct applicationonto a lithium metal anode.

It would be advantageous to be able to prepare electrochemical cellshaving separators with ultrafine pores and with reduced thicknesses ofless than 15 microns that are coated in contact to one or more otherlayers of the electrochemical cell by a process of coating withoutcracking or other non-uniformities in the separator that may lead toshort circuiting.

SUMMARY OF THE INVENTION

One aspect of the present invention pertains to methods of preparing acathode/separator assembly of an electrochemical cell, wherein thecathode/separator assembly comprises a cathode comprising a cathodeactive layer and a microporous separator layer, which methods comprisethe steps of (a) coating a first protective coating layer on a temporarycarrier substrate, wherein the first protective coating layer has afirst surface in contact with the temporary carrier substrate and has asecond surface on the side opposite from the temporary carriersubstrate; (b) coating a microporous separator layer on the secondsurface of the first protective coating layer, wherein the separatorlayer has a first surface in contact with the second surface of thefirst protective coating layer and has a second surface on the sideopposite from the first protective coating layer; (c) laminating a firstsurface of the cathode in a desired adhesion pattern on the secondsurface of the separator layer; and (d) removing the temporary carriersubstrate from the first protective coating layer to form thecathode/separator assembly.

Another aspect of the present invention pertains to methods of preparinga cathode/separator assembly of an electrochemical cell, wherein thecathode/separator assembly comprises a cathode active layer and amicroporous separator layer, which methods comprise the steps of (a)coating a first protective coating layer on a temporary carriersubstrate; (b) coating a microporous separator layer on the firstprotective coating layer; (c) coating a cathode active layer in adesired pattern on a surface of the separator layer, which surface is onthe side of the separator layer opposite from the first protectivecoating layer; and (d) removing the temporary carrier substrate from thefirst protective coating layer to form the cathode/separator assembly.

In one embodiment of the methods of preparing a cathode/separatorassembly of an electrochemical cell of the present invention, the firstprotective coating layer is a single ion conducting layer, such as, forexample, a single ion conducting layer that only conducts lithium ionsin a lithium electrochemical cell, but does not transport electrolytesolvents, ionic electrolyte salts, and other materials besides lithiumions. Suitable single ion conducting layers include, but are not limitedto, glassy layers comprising a glassy material selected from the groupconsisting of lithium silicates, lithium borates, lithium aluminates,lithium phosphates, lithium phosphorus oxynitrides, lithiumsilicosulfides, lithium germanosulfides, lithium lanthanum oxides,lithium titanium oxides, lithium borosulfides, lithium aluminosulfides,and lithium phosphosulfides. In a preferred embodiment, the single ionconducting layer comprises a lithium phosphorus oxynitride. In oneembodiment, the first protective coating layer is an ionicallyconductive layer which is impervious to dimethoxyethane and1,3-dioxolane, and to combinations thereof. In one embodiment, the firstprotective coating layer comprises a polymer selected from the groupconsisting of electrically conductive polymers, ionically conductivepolymers, sulfonated polymers, and hydrocarbon polymers. In oneembodiment, the first protective coating layer comprises an electricallyconductive pigment. In one embodiment, the first protective coatinglayer comprises an aromatic hydrocarbon.

In one embodiment of the methods of preparing a cathode/separatorassembly of this invention, the separator layer comprises one or moremicroporous xerogel layers. In one embodiment, the cathode/separatorassembly further comprises a second protective coating layer, whereinthe second protective coating layer is in contact with at least one ofthe one or more microporous xerogel layers of the separator layer. Inone embodiment, one of the one or more protective coating layers of thecathode/separator assembly is coated directly on the temporary carriersubstrate, and one of the one or more microporous xerogel layers of themicroporous separator layer is then coated on a surface of the one ofthe one or more protective coating layers, which surface is on the sideof the one of the one or more protective coating layers opposite fromthe temporary carrier substrate, and further wherein the temporarycarrier substrate is removed in step (c) from the surface of the one ofthe one or more protective coating layers, which surface is on the sideof the one of the one or more protective coating layers opposite fromthe separator layer. In one embodiment, the second protective coatinglayer of the cathode/separator assembly is coated in step (b) directlyon the surface of the first protective coating layer, which surface ison the side of the first protective coating layer opposite from thetemporary carrier substrate layer, prior to coating the cathode activelayer. In one embodiment, the second protective coating layer is asingle ion conducting layer. In one embodiment, the second protectivecoating layer is an ionically conductive layer which is impervious todimethoxyethane and 1,3-dioxolane and combinations thereof.

In a preferred embodiment of the methods of preparing acathode/separator assembly of this invention, the separator layercomprises one or more microporous pseudo-boehmite layers. In a morepreferred embodiment, the cathode/separator assembly further comprises asecond protective coating layer, wherein the second protective coatinglayer is in contact with at least one of the one or more microporouspseudo-boehmite layers of the separator layer. In one embodiment, thesecond protective coating layer is coated directly on the firstprotective coating layer, and one of the one or more microporouspseudo-boehmite layers of the microporous separator layer is then coatedon a surface of the second protective coating layer, which surface ofthe second protective coating layer is on the side opposite from thefirst protective coating layer. In one embodiment, the second protectivecoating layer is coated in step (b) directly on the surface of one ofthe one or more microporous pseudo-boehmite layers of the separatorlayer, prior to coating the cathode active layer. In one embodiment, thesecond protective coating layer is a single ion conducting layer. In oneembodiment, the second protective coating layer is an ionicallyconductive layer which is impervious to dimethoxyethane and1,3-dioxolane and combinations thereof.

In one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, the temporary carrier substrate is aflexible web substrate. Suitable web substrates include, but are notlimited to, papers, polymeric films, and metals. In one embodiment, theflexible web substrate is surface treated with a release agent.

In one embodiment of the methods of preparing a cathode/separatorassembly of this invention, the cathode active layer comprises anelectroactive material selected from the group consisting ofelectroactive metal chalcogenides, electroactive conductive polymers,and electroactive sulfur-containing materials, and combinations thereof.In one embodiment, the cathode active layer comprises elemental sulfur.In one embodiment, the cathode active layer comprises an electroactivesulfur-containing organic polymer, wherein the polymer, in its oxidizedstate, comprises one or more polysulfide moieties selected from thegroup consisting of: —S_(m)—, —S_(m) ⁻, and S_(m) ²⁻; where m is aninteger equal to or greater than 3.

In one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, the desired pattern of the cathodeactive layer does not completely coat or cover the surface of theseparator layer, which surface is on the side of the separator layeropposite from the first protective coating layer. In one embodiment, thedesired pattern of the cathode active layer does not completely coat thesecond surface of the second protective coating layer when the secondprotective coating layer is coated onto the separator layer.

In one embodiment, the methods further comprise a step of coating anedge insulating layer in a desired pattern on the surface of theseparator layer. In one embodiment, the step of coating the edgeinsulating layer occurs subsequent to the steps of coating the firstprotective coating, microporous separator, and cathode active layers andprior to the step of removing the temporary carrier substrate from thefirst protective coating layer. In one embodiment, the desired patternof the edge insulating layer comprises substantially the remaining areaof the surface of the separator layer that is not coated with thedesired pattern of the cathode active layer. In one embodiment, aportion of the desired pattern of the edge insulating layer is incontact with a portion of the desired pattern of the cathode activelayer. In one embodiment, the thickness of the edge insulating layer issubstantially the same as the thickness of the cathode active layer. Inone embodiment, the step of coating the edge insulating layer occurssubsequent to the step of coating the first protective coating andmicroporous separator layers and prior to the steps of coating thecathode active layer and removing the temporary carrier substrate fromthe first protective coating layer. In one embodiment, the edgeinsulating layer comprises an insulating xerogel layer. In oneembodiment, the edge insulating layer comprises an insulatingnon-porous, polymeric layer. In one embodiment, the edge insulatinglayer is a single ion conducting layer. In one embodiment, the edgeinsulating layer is an ionically conductive layer which is impervious todimethoxyethane and 1,3-dioxolane and combinations thereof.

In one embodiment of the methods of preparing a cathode/separatorassembly of this invention, the methods further comprise a step ofdepositing a cathode current collector layer in a desired pattern on thesurface of the cathode active layer, which surface is on the sideopposite from the separator layer. In one embodiment, the step ofdepositing the cathode current collector layer occurs subsequent to thesteps of coating the first protective coating, microporous separator,and cathode active layers and prior to the step of removing thetemporary carrier substrate from the first protective coating layer. Inone embodiment, the methods further comprise a step of coating anelectrode insulating layer in a desired pattern on the surface of thecathode current collector layer, which surface is on the side oppositefrom the cathode active layer. In one embodiment, the methods furthercomprise a step of depositing an anode current collector layer in adesired pattern on the electrode insulating layer.

In one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, the methods further comprise a stepof depositing a cathode current collector layer in a desired pattern onthe outer surface of the cathode active layer and, optionally, on theouter surface of the edge insulating layer. In one embodiment, the stepof depositing the cathode current collector layer occurs subsequent tothe steps of coating the first protective coating, microporousseparator, cathode active, and edge insulating layers, and prior to thestep of removing the temporary carrier substrate from the firstprotective coating layer. In one embodiment, the step of depositing thecathode current collector layer occurs subsequent to the steps ofcoating the first protective coating, microporous separator, and cathodeactive layers, prior to the step of coating the edge insulating layer,and prior to the step of removing the temporary carrier substrate fromthe first protective coating layer. In one embodiment, the methodsfurther comprise a step of coating an electrode insulating layer in adesired pattern on the outer surface of the cathode current collectorlayer and, optionally, on the outer surface of the edge insulatinglayer.

One aspect of this invention pertains to methods of preparing anelectrochemical cell, which methods comprise the steps of (a) providinga cathode/separator assembly prepared by a method comprising the stepsof: (i) optionally coating a first protective coating layer on atemporary carrier substrate, wherein the first protective coating layerhas a first surface in contact with the temporary carrier substrate andhas a second surface on the side opposite from the temporary carriersubstrate, (ii) coating a microporous separator layer on the secondsurface of the first protective coating layer, wherein the separatorlayer has a first surface in contact with the second surface of thefirst protective coating layer, or of the temporary carrier substrate ifno first protective coating is present, (iii) laminating a first surfaceof a cathode in a desired adhesion pattern on the second surface of theseparator layer, wherein the cathode comprises a cathode active layer,and (iv) removing the temporary carrier substrate from the first surfaceof the first protective coating layer, or from the first surface of theseparator layer if no first protective coating is present; providing ananode; and providing an electrolyte, wherein the electrolyte iscontained in the pores of the separator; wherein the first surface ofthe first protective coating layer, or the first surface of theseparator layer if no first protective coating layer is present, of thecathode/separator assembly and the anode are positioned in aface-to-face relationship.

Another aspect of the present invention pertains to methods of preparingan electrochemical cell, which methods comprise the steps of: (a)providing a cathode/separator assembly prepared by a method comprisingthe steps of (i) coating a first protective coating layer on a temporarycarrier substrate, as described herein; (ii) coating a microporousseparator layer on the first protective coating layer; (iii) coating acathode active layer, as described herein, in a desired pattern on asurface of the separator layer, which surface is on the side of theseparator layer opposite from the first protective coating layer, and(iv) removing the temporary carrier substrate from the first protectivecoating layer to form the cathode/separator assembly; (b) providing ananode; (c) providing a cathode current collector layer; (d) providing anelectrode insulating layer interposed between the anode and the cathodecurrent collector layer; and (e) providing an electrolyte, wherein theelectrolyte is contained in the pores of the separator layer; andwherein the first protective coating layer of the cathode/separatorassembly and the anode are positioned in a face-to-face relationship andthe cathode active layer and the cathode current collector layer arepositioned in a face-to-face relationship.

In one embodiment of the methods of preparing an electrochemical cell ofthe present invention, the first protective coating layer is a singleion conducting layer. In one embodiment, the first protective coatinglayer is an ionically conductive layer which is impervious todimethoxyethane and 1,3-dioxolane and combinations thereof. In oneembodiment, the separator layer comprises one or more microporousxerogel layers. In one embodiment, the cathode/separator assemblyfurther comprises a second protective coating layer, wherein the secondprotective coating layer is in contact with at least one of the one ormore microporous xerogel layers of the separator layer. In oneembodiment, the second protective coating layer is a single ionconducting layer. In one embodiment, the second protective coating layeris an ionically conductive layer which is impervious to dimethoxyethaneand 1,3-dioxolane, and to combinations thereof.

In a preferred embodiment of the methods of preparing an electrochemicalcell of this invention, the separator layer comprises one or moremicroporous pseudo-boehmite layers. In a more preferred embodiment, theelectrochemical cell further comprises a second protective coatinglayer, wherein the second protective coating layer is in contact with atleast one of the one or more microporous pseudo-boehmite layers of theseparator layer.

In one embodiment of the methods of preparing an electrochemical cell ofthis invention, the anode comprises an anode active material selectedfrom the group consisting of lithium metal, lithium-aluminum alloys,lithium-tin alloys, lithium-intercalated carbons, andlithium-intercalated graphites. Suitable electrolytes include liquidelectrolytes, gel polymer electrolytes, solid polymer electrolytes, andsingle ion conducting electrolytes. In one embodiment, the electrolytecomprises a liquid electrolyte.

In one embodiment of the methods of preparing an electrochemical cell ofthe present invention, the electrode insulating layer comprises apolymeric plastic film. In one embodiment, the electrode insulatinglayer comprises a polymeric coating.

In one embodiment of the methods of preparing an electrochemical cell ofthis invention, the cell is a secondary cell. In one embodiment of themethods of preparing an electrochemical cell of this invention, the cellis a primary cell.

Another aspect of the present invention pertains to methods of preparingan electrochemical cell, which methods comprise the steps of (a) coatinga first protective coating layer on a temporary carrier substrate, asdescribed herein; (b) coating a microporous separator layer, asdescribed herein, on the first protective coating layer, (c) coating acathode active layer, as described herein, in a desired pattern on asurface of the separator layer, which surface is on the side of theseparator layer opposite from the first protective coating layer; (d)depositing a cathode current collector layer in a desired pattern on thecathode active layer, which surface is on the side of the cathode activelayer opposite from the separator layer; (e) depositing an electrodeinsulating layer in a desired pattern on a surface of the cathodecurrent collector layer, which surface is on the side of the cathodecurrent collector layer opposite from the cathode active layer; (f)depositing an anode current collector layer in a desired pattern on asurface of the electrode insulating layer, which surface is on the sideof the electrode insulating layer opposite from the cathode currentcollector layer, (g) depositing an anode active material layer in adesired pattern on a surface of the anode current collector layer, whichsurface is on the side of the anode current collector layer oppositefrom the electrode insulating layer; (h) removing the temporary carriersubstrate from the first protective coating layer; and (i) providing anelectrolyte, wherein the electrolyte is contained in the pores of theseparator layer. In one embodiment, step (g) of the methods furthercomprises depositing an anode protective coating layer on the anodeactive material. In one embodiment, the anode protective coating layeris a single ion conducting layer. Suitable single ion conducting layersfor the anode protective coating layer include, but are not limited to,glassy layers comprising a glassy material selected from the groupconsisting of lithium silicates, lithium borates, lithium aluminates,lithium phosphates, lithium phosphorus oxynitrides, lithiumsilicosulfides, lithium germanosulfides, lithium lanthanum oxides,lithium titanium oxides, lithium borosulfides, lithium aluminosulfides,and lithium phosphosulfides. In a preferred embodiment, the single ionconducting layer comprises a lithium phosphorus oxynitride. In oneembodiment, the anode protective coating layer is an ionicallyconductive layer which is impervious to dimethoxyethane and1,3-dioxolane, and combinations thereof. In one embodiment, the anodeprotective coating layer comprises a polymer selected from the groupconsisting of electrically conductive polymers, ionically conductivepolymers, sulfonated polymers, and hydrocarbon polymers. In oneembodiment, the anode protective coating layer comprises an electricallyconductive pigment. In one embodiment, the anode protective coatinglayer comprises an aromatic hydrocarbon. In one embodiment, the anodeprotective coating layer comprises a metal, such as copper, that formsan alloy with lithium.

Another aspect of this invention pertains to methods of preparing anelectrochemical cell comprising a casing and a multilayer cell stack,which methods comprise the steps of (a) providing a laminar combinationof: (i) an anode assembly comprising an anode having an anode activelayer; wherein the anode active layer comprises an anode active materialcomprising lithium, a first cathode current collector layer, and anelectrode insulating layer interposed between the anode and the firstcathode current collector layer; and (ii) a cathode/separator assemblycomprising a first protective coating layer; a microporous separatorlayer underlying the first protective coating layer; a cathode activelayer in a first desired coating pattern on a surface of the microporousseparator layer, which surface is on the side of the separator layeropposite from the first protective coating layer; and an edge insulatinglayer in a second desired coating pattern on the surface of theseparator layer; wherein the first cathode current collector layer andthe cathode active layer are positioned in a face-to-face relationship;(b) winding the laminar combination to form an anode-electrodeinsulating layer-first cathode current collector layer-cathode/separatorassembly multilayer cell stack, wherein the first cathode currentcollector layer is in contact with the cathode active layer; (c)providing an electrolyte, wherein the electrolyte is contained in thepores of the separator layer; (d) providing a casing to enclose the cellstack; and (e) sealing the casing. In one embodiment, the anode furthercomprises an anode current collector layer interposed between the anodeactive layer and the electrode insulating layer. In one embodiment, asecond cathode current collector layer is deposited in a third desiredpattern on the outer surface of the cathode active layer and on theouter surface of the edge insulating layer.

In one embodiment of the methods of preparing an electrochemical cell ofthis invention, the cathode/separator assembly of step (a) furthercomprises a temporary carrier substrate on a surface of the firstprotective coating layer, which surface is on the side of the firstprotective coating layer opposite from the separator layer, and themethods further comprise a step of removing the temporary carriersubstrate from the first protective coating layer prior to completion ofstep (b). In one embodiment, a second cathode current collector layer isdeposited in a third desired coating pattern on the outer surface of thecathode active layer and on the outer surface of the edge insulatinglayer.

In one embodiment of the methods of preparing an electrochemical cell ofthe present invention, the anode of the anode assembly and the firstprotective coating layer of the cathode/separator assembly arepositioned in a face-to-face relationship in step (a), and a firstcathode current collector layer-electrode insulatinglayer-anode-cathode/separator assembly multilayer cell stack is formedin step (b). In one embodiment, a second cathode current collector layeris deposited in a third desired coating pattern on the outer surface ofthe cathode active layer and on the outer surface of the edge insulatinglayer. In one embodiment, the cathode/separator assembly of step (a)further comprises a temporary carrier substrate on a surface of thefirst protective coating layer, which surface is on the side of thefirst protective coating layer opposite from the separator layer, andthe methods further comprise a step of removing the temporary carriersubstrate from the first protective coating layer prior to completion ofstep (b). In one embodiment, a second cathode current collector layer isdeposited in a third desired coating pattern on the outer surface of thecathode active layer and on the outer surface of the edge insulatinglayer.

In one embodiment of the methods of preparing an electrochemical cell ofthis invention, the first protective coating layer is a single ionconducting layer. In one embodiment, the first protective coating layeris an ionically conductive layer which is impervious to dimethoxyethaneand 1,3-dioxolane and combinations thereof. In one embodiment, theelectrochemical cell is a secondary cell. In one embodiment, theelectrochemical cell is a primary cell.

Another aspect of this invention pertains to methods of preparing anelectrochemical cell comprising a casing and a multilayer cell stack,which methods comprise the steps of (a) providing a laminar combinationof: (i) an anode assembly comprising an anode comprising lithium metal;and, (ii) a cathode/separator assembly comprising a first protectivecoating layer, a microporous separator layer underlying the firstprotective coating layer, a cathode active layer in a first desiredcoating pattern on a surface of the microporous separator layer, whichsurface is on the side of the separator layer opposite from the firstprotective coating layer, and an edge insulating layer in a seconddesired coating pattern on the surface of the separator layer; a cathodecurrent collector layer in a third desired coating pattern on the outersurface of the cathode active layer and on the outer surface of the edgeinsulating layer; an electrode insulating layer in a fourth desiredcoating pattern on the outer surface of the cathode current collectorlayer and on the outer surface of the edge insulating layer; wherein theanode and the electrode insulating layer are positioned in aface-to-face relationship; (b) winding the laminar combination to forman anode-electrode insulating layer-cathode current collectorlayer-cathode/separator assembly multilayer cell stack, wherein thecathode current collector layer is in contact with the cathode activelayer; (c) providing an electrolyte, wherein the electrolyte iscontained in the pores of the separator layer; (d) providing a casing toenclose the cell stack; and (e) sealing the casing. In one embodiment,the cathode/separator assembly of step (a) further comprises a temporarycarrier substrate on a surface of the first protective coating layer,which surface is on the side of the first protective coating layeropposite from the separator layer, and the methods further comprise astep of removing the temporary carrier substrate from the firstprotective coating layer prior to completion of step (b). In oneembodiment, the anode and the first protective coating layer of thecathode/separator assembly are positioned in a face-to-face relationshipin step (a), and an anode-cathode/separator assembly-cathode currentcollector layer-electrode insulating layer multilayer cell stack isformed in step (b).

Another aspect of this invention pertains to methods of preparinganode/separator assemblies, as described herein, and tocathode/separator assemblies and to anode/separator assemblies preparedaccording to the methods of this invention, as described herein. Anotheraspect of the present invention pertains to electrochemical cellsprepared according to the methods of the present invention, as describedherein.

As will be appreciated by one of skill in the art, features of oneaspect or embodiment of the invention are also applicable to otheraspects or embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, which comprises a first protectivelayer coating step 40, a microporous separator coating step 50, acathode active layer coating step 60, and a temporary carrier substrateremoving step 70.

FIG. 2 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, which comprises a protective coatingstep 40, a microporous separator coating step 50, a cathode active layercoating step 60, and a temporary carrier substrate removing step 70.

FIG. 3 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing a cathode/separatorassembly of this invention, which further comprises a protective coatinglayer step 41 prior to the cathode active layer coating step 60, incomparison to the embodiment illustrated in FIG. 1.

FIG. 4 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, which further comprises an edgeinsulating layer coating step 62 subsequent to the cathode active layercoating step 60 and also comprises a slitting step 95 subsequent to thetemporary carrier substrate removal step 70, in comparison to theembodiment illustrated in FIG. 1.

FIG. 5 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing a cathode/separatorassembly of this invention, which further comprises an edge insulatinglayer coating step 62 prior to the cathode active layer coating step 60,in comparison to the embodiment illustrated in FIG. 1.

FIG. 6 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, which further comprises a cathodecurrent collector layer coating step 80 and an edge insulating layercoating step 62 prior to the temporary carrier substrate removing step70, in comparison to the embodiment illustrated in FIG. 1.

FIGS. 7A and 7B show representative process flow diagrams withcross-sectional views of two other embodiments of the methods ofpreparing a cathode/separator assembly of this invention, which furthercomprises, for FIG. 7A, a cathode current collector layer coating step80 prior to the temporary carrier substrate removing step 70, incomparison to the embodiment illustrated in FIG. 4; and which furthercomprises, for FIG. 7B, a cathode current collector layer coating step80 and a slitting step 95 prior to the temporary carrier substrateremoving step 70, in comparison to the embodiment illustrated in FIG. 5.

FIGS. 8A and 8B show representative process flow diagrams withcross-sectional views of two other embodiments of the methods ofpreparing a cathode/separator assembly of the present invention, whichfurther comprises, for FIG. 8A, an electrode insulating layer coatingstep 90 prior to the temporary carrier substrate removing step 70, incomparison to the embodiment illustrated in FIG. 7A; and which furthercomprises, for FIG. 8B, an electrode insulating layer coating step 90prior to the slitting step 95, in comparison to the embodimentillustrated in FIG. 7B.

FIG. 9 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing an electrochemicalcell of this invention, which comprises a combining step 100 utilizing acathode/separator assembly 31 as one element, a winding step 110, and anelectrolyte filling and sealing step 120.

FIG. 10 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing an electrochemicalcell of this invention, which comprises a combining step 100 utilizing acathode/separator assembly 32 as one element, a winding step 110, and anelectrolyte filling and sealing step 120.

FIG. 11 shows a representative process flow diagram with cross-sectionalviews of one embodiment of the methods of preparing an electrochemicalcell of the present invention, which comprises a combining step 100utilizing an anode active layer 701 as one element and acathode/separator assembly 47 as a second element, a winding step 110,and an electrolyte filling and sealing step 120.

FIG. 12 shows a representative flow diagram with cross-sectional viewsof one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, which comprises a laminating step 75utilizing a composite 24 of a temporary carrier substrate, a protectivecoating layer, and a separator layer as one element and a composite 44of a substrate, a cathode current collector layer, and a cathode activelayer as a second element, and a temporary carrier substrate removingstep 70.

DETAILED DESCRIPTION OF THE INVENTION

Many microporous coatings, particularly microporous xerogel coatingswhich are typically subject to a high level of stresses and potentialcracking during drying, formation, and mechanical handling of thethree-dimensional gel structure in the microporous layer, are difficultto obtain at the desired quality level when coated on surfaces which arerough and non-uniform or which have poor mechanical strength andflexibility properties. Also, many thin coatings, such as on the orderof 10 microns or less and particularly when the coating layer thicknessis about 2 microns or less, are similarly difficult to obtain as uniformand continuous layers when coated on surfaces which are rough andnon-uniform or which have poor mechanical strength and flexibilityproperties. A rough and non-uniform coating surface may cause a widevariation in the thicknesses of microporous, thin, and other coatingsapplied to this surface. Besides possibly causing the formation ofsections of the coating layer which are too thin or too thick for thedesired application, these thickness variations may interfere with thedesired level and uniformity of the microporosity and other propertiesand with the mechanical strength and cracking resistance of themicroporous and other layers. The tendency for reduced mechanicalflexibility and cracking may be particularly true when the thickness ofa microporous coating layer is significantly above that needed for thedesired application. Also, a coating surface with poor mechanicalstrength and flexibility may induce, for example, stresses, mechanicalfailure, poor adhesion, and cracking in a microporous or other layercoated on this surface.

Examples of applications for microporous and other coatings, includingmicroporous xerogel coatings, where a relatively smooth surface and amechanically strong layer on which to apply and form the microporous orother coatings would be useful, include, but are not limited to,microporous separators and other layers for contact to one or moreelectrodes of an electrochemical cell; microporous ink jet ink-receptivelayers for contact to a wide variety of rough, uneven support surfacessuch as papers, fabrics, canvas, and spun-woven plastics; andmicroporous filtration layers for contact to a wide variety of rough,uneven substrates such as papers. For example, for the productapplication of microporous separators and other layers involving contactto the positive electrode or cathode of an electrochemical cell, theroughness and non-uniformity of the cathode surface prior to coating themicroporous separator or other layer on it may be reduced, for example,by calendering the cathode surface or by applying a thin uniform coatingto the cathode surface. However, the reduction of the roughness andnon-uniformity of the cathode surface by these approaches may still notbe sufficient and also may not prevent undesirable results from poormechanical strength and flexibility of the cathode and from penetrationof the separator or other coating into porous areas of the cathodeduring the coating application process.

Also, for example, for the product application of microporous separatorsand other layers involving contact to the negative electrode or anode ofan electrochemical cell, the roughness and non-uniformity of the anodesurface prior to coating the microporous separator or other layer on itmay be reduced, for example, by calendering the anode surface or byapplying a thin uniform coating to the anode surface. However, thereduction of the roughness and non-uniformity of the anode surface bythese approaches may still not be sufficient and also may not preventundesirable results from poor mechanical strength and flexibility of theanode and from penetration of the separator or other coating into porousareas of the anode during the coating application process. Also,particularly in the case of chemically reactive anodes, such as lithiummetal anodes, the separator coating may have components which are tooreactive to coat onto the anode without resulting in degradation of theanode active layer.

The present invention overcomes these limitations for preparingmicroporous and other coatings for a wide variety of applications, suchas separators and protective coating layers for use in electrochemicalcells, ink jet ink-receptive media, filtration materials, and otherproduct applications. One aspect of the present invention pertains tomethods of preparing an electrochemical cell, which methods comprise thesteps of (a) coating a protective coating layer on a temporary carriersubstrate, (b) coating a microporous separator layer on the protectivecoating layer, (c) coating a cathode active layer and any other desiredlayers in desired coating patterns built up on the surface of theseparator layer on the side opposite from the protective coating layer,(d) laminating or contacting the cathode/separator assembly resultingfrom steps (a), (b), and (c) to a desired substrate, such as an anodeassembly comprising an anode active layer, and (e) removing thetemporary carrier substrate from the protective coating layer beforestep (d) or, alternatively, after step (d). The surface of the temporarycarrier substrate is selected to have the smoothness, mechanicalstrength, flexibility, and porosity properties that are desirable forthe preparation of the protective coating, and any subsequentmicroporous and other coating layers, by coating on the surface of thesubstrate and to also have suitable release properties for removal ofthe temporary carrier substrate in step (e).

Another aspect of the present invention pertains to methods of preparingan electrochemical cell, which methods comprise the steps of (a) coatinga microporous separator layer on a temporary carrier substrate, (b)optionally coating a protective coating layer on the microporousseparator layer, (c) coating or laminating an anode and any otherdesired layers in desired coating patterns built up on the surface ofthe separator layer on the side opposite from the temporary carriersubstrate, (d) laminating or contacting the anode/separator assemblyresulting from steps (a), (b), and (c) to a desired substrate, such asan cathode comprising a cathode active layer, and (e) removing thetemporary carrier substrate from the protective coating layer beforestep (d) or, alternatively, after step (d).

This method of applying a protective coating layer or a microporouslayer to a temporary carrier substrate, subsequent coating of one ormore other layers overlying the protective coating or microporouslayers, and the subsequent removal of the temporary carrier substratefrom the protective coating or microporous layer is particularly usefulwhen the protective coating layer is thin, such as a thickness less than2 microns, and when the microporous layer comprises one or moremicroporous xerogel layers. Besides applications in electrochemicalcells, this method may be readily adapted for a wide variety of otherproduct applications, including ink jet ink-receptive media andfiltration materials, where microporous and thin coating layers may beutilized.

Methods of Preparing a Cathode/Separator Assembly

One aspect of the present invention pertains to methods of preparing acathode/separator assembly of an electrochemical cell, wherein thecathode/separator assembly comprises a cathode active layer and amicroporous separator layer, which methods comprise the steps of (a)coating a first protective coating layer on a temporary carriersubstrate, wherein the first protective coating layer has a firstsurface in contact with the temporary carrier substrate and has a secondsurface on the side opposite from the temporary carrier substrate; (b)coating a microporous separator layer on the second surface of the firstprotective coating layer, wherein the separator layer has a firstsurface in contact with the second surface of the first protectivecoating layer and has a second surface on the side opposite from thefirst protective coating layer; (c) coating a cathode active layer in adesired pattern on the second surface of the separator layer, whereinthe cathode active layer has a first surface in contact with the secondsurface of the separator layer and has a second surface on the sideopposite from the separator layer; and (d) removing the temporarycarrier substrate from the first surface of the first protective coatinglayer to form the cathode/separator assembly.

One embodiment of this aspect of the present invention is illustrated inFIG. 1. Referring to FIG. 1 (not drawn to scale), in a protectivecoating step 40, a first protective coating layer 101 is coated unto asurface of a temporary carrier substrate 2 to form composite 14. Next,in a microporous separator coating step 50, a microporous separatorlayer 102 is coated onto the surface of the first protective coatinglayer 101 to form composite 15 comprising temporary carrier substrate 2,first protective coating layer 101, and microporous separator layer 102.Next, in a cathode active layer coating step 60, a cathode active layer201 is coated in a desired pattern onto the surface of the microporousseparator layer 102 to form composite 10 comprising temporary carriersubstrate 2, first protective coating layer 101, microporous separatorlayer 102, and cathode active layer 201. Following this step, in atemporary carrier substrate removing step 70, the temporary carriersubstrate 2 is removed from the first protective coating layer 101 ofcomposite 10 to form cathode/separator assembly 51 comprising firstprotective coating layer 101, microporous separator layer 102, andcathode active layer 201.

The incorporation of a first protective coating layer in thecathode/separator assembly of the methods of this invention enhances themechanical strength and adds flexibility to microporous separator layerscomprising one or more microporous layers, particularly those separatorlayers comprising one or more microporous xerogel layers. Also,importantly, the first protective coating layer by virtue of itspositioning between the anode and the separator of the electrolyteelement in the electrochemical cell may function to reduce or eliminatedegradation of the anode by contact with electrolyte solvents,electrolyte salts, cathode reduction products, and other materials ofthe electrolyte and cathode parts of the cell. For example, the firstprotective coating layer may encapsulate the outer surfaces of thecathode/separator assembly and act as a barrier to migration ofundesired materials to the surface of the anode, such as the lithiumsurface. This barrier may be a single ion conducting layer which allowsthe necessary movement of lithium ions for the functioning of the cellbut which does not allow, or greatly inhibits, the movement of anions,such as anions of the electrolyte salts and any anions formed by thecathode active materials, such as polysulfide and sulfide anions in thecase of electroactive sulfur-containing cathodes. Also, this barrier maybe an impermeable barrier against solvents such that the barrier doesnot allow, or greatly inhibits, the movement of electrolyte solvents,and any dissolved materials in these solvents, to the surface of theanode. To achieve this functioning as a barrier layer to protect theanode, the first protective coating layer typically is not microporous.

Also, in an assembled cell, the first protective coating layer may bedirectly in contact with the anode surface and thereby provideprotection for the anode. Although protection for the anode may beprovided, for example, by conductive polymer coating layers or singleion conducting layers coated directly on the anode, it may be moredesirable and effective to provide the protective layers for the anodeas an outer layer of the separator and electrolyte element on the sideopposite from the cathode. This configuration in an assembled cell maymore effectively accommodate the changes during charge and dischargecycles of the cell, such as, for example, thickness and surface changesof the anode during charge and discharge cycles.

In one embodiment, the first protective coating layer is a single ionconducting layer. Single ion conducting layers have the capability ofexclusively transporting cations, such as lithium ions, and may comprisepolymers such as, for example, disclosed in U.S. Pat. No. 5,731,104 toVentura, et al. Suitable single ion conducting layers include, but arenot limited to, glassy layers comprising a glassy material selected fromthe group consisting of lithium silicates, lithium borates, lithiumaluminates, lithium phosphates, lithium phosphorus oxynitrides, lithiumsilicosulfides, lithium germanosulfides, lithium lanthanum oxides,lithium titanium oxides, lithium borosulfides, lithium aluminosulfides,and lithium phosphosulfides. In a preferred embodiment, the single ionconducting layer comprises a lithium phosphorus oxynitride. Electrolytefilms of lithium phosphorus oxynitride are disclosed, for example, inU.S. Pat. No. 5,569,520 to Bates. A thin film layer of lithiumphosphorus oxynitride interposed between a lithium anode and anelectrolyte is disclosed, for example, in U.S. Pat. No. 5,314,765 toBates.

In one embodiment, the first protective coating layer is an ionicallyconductive layer which is impervious to dimethoxyethane and1,3-dioxolane and combinations thereof. The barrier properties totransport of solvents of this ionically conductive layer may be obtainedfrom a variety of ionically conductive layers as, for example, bycrosslinking by heat, radiation, or use as a crosslinking agent a highmolecular weight, ionically conductive polyether, such as a hydroxyethylacrylate ester of a methylvinylether-maleic anhydride polymer. Thesecrosslinked polymers may also be capable of absorbing large quantitiesof typical electrolyte solvents for lithium cells, such asdimethoxyethane and 1,3-dioxolane, to form a gelled barrier to transportof electrolyte liquids through the protective coating layer.

In one embodiment, the first protective coating layer comprises apolymer selected from the group consisting of electrically conductivepolymers, ionically conductive polymers, sulfonated polymers, andhydrocarbon polymers. Suitable conductive polymers include, but are notlimited to, those described in U.S. Pat. No. 5,648,187 to Skotheim, forexample, including, but not limited to, poly(p-phenylene),polyacetylene, poly(phenylenevinylene), polyazulene,poly(perinaphthalene), polyacenes, and poly(naphthalene-2,6-diyl).

In one embodiment, the first protective coating layer comprises anionically conductive polymer. Suitable ionically conductive polymersinclude, but are not limited to, ionically conductive polymers known tobe useful in solid polymer electrolytes and gel polymer electrolytes forlithium electrochemical cells, such as, for example, polyethylene oxidesand polydivinyl-poly(ethylene glycols). In a preferred embodiment, theionically conductive polymer is a polydivinyl-poly(ethylene glycol).

In one embodiment, the first protective coating layer comprises asulfonated polymer. Suitable sulfonated polymers include, but are notlimited to, sulfonated siloxane polymers, sulfonatedpolystyrene-ethylene-butylene polymers, and sulfonated polystyrenepolymers. In one embodiment, the sulfonated polymer is a sulfonatedpoystyrene.

In one embodiment, the first protective coating layer comprises ahydrocarbon polymer. Suitable hydrocarbon polymers include, but are notlimited to, ethylene-propylene polymers, polystyrene polymers, and thelike.

In one embodiment, the first protective coating layer comprises amicroporous xerogel layer and, preferably, the microporous xerogel layercomprises an organic polymer. Suitable materials for making themicroporous xerogel layer and for the organic polymers to be present inthe microporous xerogel layer include, but are not limited to, thematerials and organic polymers, as described herein, for use in makingthe microporous xerogel separator layers of the cathode/separatorassemblies of the present invention. Suitable materials for the xerogellayer of the protective coating layer include, but are not limited to,oxides selected from the group consisting of pseudo-boehmite, zirconiumoxide, titanium oxide, aluminum oxide, silicon oxide, and tin oxide. Ina preferred embodiment, the material of the xerogel layer of theprotective coating layer comprises pseudo-boehmite or zirconium oxide,or combinations thereof.

Since the microporous xerogel layer is typically too porous to act as asingle ion conducting protective layer or to be impervious todimethoxyethane and 1,3-dioxolane, and combinations thereof, theprotective layer may further comprise barrier materials impregnated inthe pores of the xerogel layer to both increase the cycle life of thecell by protecting the lithium against degradation by electrolyte andcathode components and to increase the manufacturability and reliabilityof the cell by mechanically protecting the separator and cathode layersagainst cracking and breaking during cell fabrication and usage.

One advantage of using microporous xerogel layers in the firstprotective coating layer is that the cationic properties of the metal ofthe oxide, such as Al³⁺, typically have a strong affinity for anions,such as the polysulfides formed during the cathode reduction cycle oflithium-sulfur cells, and may strongly adsorb these anions during theuse of the cell. These adsorbed anions will inhibit or block transportof species, other than the extremely small lithium cations which alsomay have enhanced transport from the adsorbed anions, through the firstprotective coating layer. Besides the physical blocking from thepresence of the adsorbed anions in the ultrafine pores of the xerogellayer having average pore diameters typically in the range of only 1 to4 microns, the negative charge of the adsorbed anions may also be usefulin repelling and preventing more anions from diffusing into the firstprotective coating layer.

Thus, first protective coating layers comprising a microprous xerogellayer provide a wide variety of options for protecting the cell fromdegradation of the lithium anode and reduced cycle life and also frommechanical damage during fabrication and usage which might cause shortcircuiting or other safety-related or capacity-related defects todevelop in the cell.

In one embodiment, the protective coating layer comprises a releaseagent, such as a fluorochemical compound. This is a useful way toprovide the proper level of adhesion for the protective coating layerduring fabrication while also allowing for easy delamination when it isdesired to remove the temporary carrier substrate. This also reduces oreliminates the need to treat the temporary carrier substrate with arelease agent and makes it easier to use less expensive substrates withno extra release treatment on their surfaces, such as, for example,polyethylene terephthalate (PET) films that are untreated for release oradhesion on their surfaces. In one embodiment, the release agent of thefirst protective coating layer comprises a perfluorinated moiety, suchas, for example, CF₃— and —CF₂—.

The first protective coating layer may be a single layer prepared in asingle step or prepared in two or more steps, such as, for example, inthe two step coating process of coating a microporous xerogel layer andthen impregnating the pores of the very thin xerogel layer with amonomer which subsequently is crosslinked to enhance the protectiveproperties for longer cycle life and better mechanical properties andflexibility of the layers in the cell. Also, the first protectivecoating layer may comprise two or more protective coating layers, whichprovide cycle life and mechanical protective properties in total, andare applied prior to the application of the microprous separatorcoating.

In one embodiment, the first protective coating layer comprises anelectrically conductive pigment. Suitable electrically conductivepigments include, but are not limited to, carbon blacks and conductivetin oxides. In one embodiment, the first protective coating layercomprises an aromatic hydrocarbon. Suitable aromatic hydrocarbonsinclude, but are not limited to, 9,9′-bianthryl and other dimers ofpolycyclic aromatic hydrocarbons. These materials, such as9,9′-bianthryl, may be incorporated into the protective coating layer bythe use of a more soluble precursor form, such as9-hydroxy-10,10-dihydro-9,9′-bianthryl, which is subsequently reacted toform 9,9′-bianthryl during cycling of the cell or by heating or anotherreaction process.

The term “monomer” is used herein to describe moieties which have areactive moiety and are capable of reacting to form a polymer. The term“polymer” is used herein to describe molecules that have two or morerepeating moieties formed from a monomer moiety. The term “macromonomer”is used herein to describe polymers with molecular weights from severalhundreds to tens of thousands with a functional group at a chain endthat may be polymerized. In one embodiment, the first protective coatinglayer and any other protective coating layers of the cathode/separatorassembly of the present invention comprise a polymer. In one embodiment,the polymer of the one or more protective coating layers comprises oneor more moieties from the polymerization of one or more monomers ormacromonomers. Examples of suitable monomers or macromonomers include,but are not limited to, acrylates, methacrylates, olefins, epoxides, andvinyl ethers. Further examples of suitable monomers or macromonomers forforming the polymer of the protective coating layer include, but are notlimited to, those described in U.S. patent application Ser. No.09/215,029 by Ying et al. of the common assignee, the disclosure ofwhich is fully incorporated herein by reference.

The molecular weight of the polymer of the one or more protectivecoating layers is preferably greater than 10,000. More preferred is apolymer of molecular weight greater than 50,000.

The thickness of the one or more protective coating layers of thecathode/separator assembly of the methods of this invention may varyover a wide range from about 0.01 microns to about 20 microns. In apreferred embodiment, the protective coating layer has a thickness offrom about 0.01 microns to about 10 microns. More preferred is athickness of from about 0.05 microns to about 5 microns, and even morepreferred is a thickness of from about 0.1 microns to about 2 microns,especially when multiple protective coating layers are present.Conventional separators, such as polyolefin materials, are typically 25to 50 microns in thickness so it is particularly advantageous that theprotective coating layers combined with microporous separator layers ofthe methods of this invention can be effective and inexpensive atoverall thicknesses below 15 microns. In other words, it is preferablethat the combined thickness of the one or more microporous layers, suchas microporous xerogel layers, and the one or more protective coatinglayers be below 15 microns.

The one or more protective coating layers comprising a polymer of thecathode/separator assembly of the methods of this invention may comprisea pigment. Suitable pigments for use in the one or more protectivecoating layers include, but are not limited to, colloidal silicas,amorphous silicas, surface treated silicas, colloidal aluminas,amorphous aluminas, conductive carbons, conductive tin oxides, titaniumoxides, and polyethylene beads.

The weight ratio of the polymer to the pigment in the one or moreprotective coating layers may vary from about 1:10 to about 10:1. In apreferred embodiment, the polymer and the pigment are present in the oneor more protective coating layers at a weight ratio of from about 1:4 toabout 6:1. In a more preferred embodiment, the polymer and the pigmentare present in the one or more protective coating layers at a weightratio of from about 1:3 to about 4:1.

The particle size or diameter of the pigment is preferably larger thanthe average pore diameter of the one or more microporous layers of theseparator layer so that the pigment does not penetrate pores of themicroporous separator layer, in those cases where the protective coatinglayer comprises a pigment and is coated directly onto a microporousseparator layer. The particle size of the pigment may range from about10 nm to about 10,000 nm. In a preferred embodiment, the pigment has aparticle size from about 20 nm to about 6,000 nm. In a most preferredembodiment, the pigment has a particle size from about 50 nm to about3,000 nm.

In addition to polymers and pigments, the one or more protective coatinglayers of the cathode/separator assembly of the methods of the presentinvention may comprise other additives, as known in the art of coatings,especially those known for use in flexible and durable coatings.Examples of other coating additives include, but are not limited to,photosensitizers for radiation curing of any monomers and macromonomerspresent; catalysts for non-radiation curing of any monomers,macromonomers, or polymers present; crosslinking agents such aszirconium compounds, aziridines, and isocyanates; surfactants;plasticizers; dispersants; flow control additives; and rheologymodifiers.

The microporous separator layer of the cathode/separator assembly of themethods of the present invention may have more than one microporouslayer. Also, the cathode/separator assembly of the methods of thepresent invention may have more than one protective coating layer, forexample, as illustrated in FIGS. 2 and 3. The compositions of thesemultiple microporous layers of the separator layer may be the same ordifferent for each such layer in the cathode/separator assembly. Also,the compositions of these multiple protective coating layers may be thesame or different for each such layer in the cathode/separator assembly.The many possible combinations of microporous layers and protectivecoating layers also include a protective coating layer intermediatebetween two microporous layers.

The term “electrochemical cell,” as used herein, pertains to a devicethat produces an electric current through an electrochemical reactionand that comprises a positive electrode or cathode, a negative electrodeor anode, and an electrolyte element interposed between the anode andthe cathode, wherein the electrolyte element comprises a separator layerand an aqueous or non-aqueous electrolyte in the pores of the separatorlayer.

The term “cathode active material,” as used herein, pertains to anelectrochemically active material used in the cathode active layer ofthe cathode. As used herein, the term “cathode active layer” pertains toany layer in the cathode of an electrochemical cell which comprises acathode active material.

The term “anode active material,” as used herein, pertains to anelectrochemically active material used in the anode active layer of theanode. As used herein, the term “anode active layer” pertains to anylayer in the anode of an electrochemical cell which comprises an anodeactive material.

An electrochemical cell comprising a cathode active layer with thecathode active material in an oxidized state and an anode active layerwith the anode active material in a reduced state is referred to asbeing in a charged state. Discharging an electrochemical cell in itscharged state by allowing electrons to flow from the anode to thecathode through an external circuit results in the electrochemicalreduction of cathode active material in the cathode and theelectrochemical oxidation of anode active material in the anode. Tofacilitate the efficient flow of electrons through this externalcircuit, an electrically conductive current collector layer may beplaced in contact with the surface of each electrode on the sideopposite to the electrolyte element. The term “cathode current collectorlayer,” as used herein, pertains to an electrically conductive currentcollector layer in contact with the cathode active layer. The term“cathode,” as used herein, pertains to the combination of the cathodeactive layer and the cathode current collector layer. The term “anodecurrent collector layer,” as used herein, pertains to an electricallyconductive current collector layer in contact with the anode activelayer. The term “anode,” as used herein, pertains to the anode activelayer and also to the anode current collector layer, if one is present.These current collectors are useful in efficiently collecting theelectrical current generated throughout the respective electrodes and inproviding an efficient surface for attachment of the electrical contactsleading to the external circuit.

The term “microporous” as used herein, pertains to the material of alayer, which material possesses pores of diameter of about 1 micron orless which are interconnected in a substantially continuous fashion fromone outermost surface of the layer through to the other outermostsurface of the layer. The term “microporous separator layer” is usedherein to describe a separator layer, which layer may comprise one ormore discrete coating layers, where the separator layer as a whole ismicroporous. Examples of microporous materials useful in the microporousseparator layer of the methods of the present invention include, but arenot limited to, inorganic xerogel layers or films, inorganic xerogellayers or films further comprising an organic polymer, and organicpolymer layers or films that undergo vesiculation or pore formation upongas formation, for example, by heating or photoirradiating an aromaticdiazonium compound or other gas forming compound or by heating apolymeric microcapsule containing a gas, such as isobutane.

In one embodiment of the methods of preparing a cathode/separatorassembly of this invention, the microporous separator layer comprisesone or more microporous xerogel layers. By the terms “xerogel layer” and“xerogel structure,” as used herein, is meant, respectively, a layer ofa coating or the structure of a coating layer in which the layer andstructure were formed by drying a liquid sol or sol-gel mixture to forma solid gel matrix as, for example, described in Chem. Mater., Vol. 9,pages 1296 to 1298 (1997) by Ichinose et al. for coating layers ofmetal-oxide based xerogels. Thus, if the liquid of the gel formed in theliquid sol-gel mixture is removed substantially, for example, thoughformation of a liquid-vapor boundary phase, the resulting gel layer orfilm is termed, as used herein, a xerogel layer. As the liquid isremoved from the gel in the liquid sol-gel mixture by, for example,evaporation, large capillary forces are exerted on the pores, forming acollapsed structure for the xerogel layer. The pore sizes of the xerogellayer and structure are very small, having average pore diameters lessthan 300 nm or 0.3 microns.

Thus, the microporous xerogel layer of the methods of this inventioncomprises a dried microporous three-dimensional solid gel network in asubstantially continuous fashion from one outermost surface of the layerthrough to the other outermost surface of the layer. A continuousxerogel coating layer has the materials of the xerogel in a continuousstructure in the coating layer, i.e., the materials are in contact anddo not have discontinuities in the structure, such as a discontinuouslayer of solid pigment particles that are separated from each other, forexample, by a polymer binder between the individual pigment particles.In contrast, xerogel pigment particles may be formed by a xerogelprocess involving drying a liquid solution of a suitable precursor tothe pigment in order to form a dried mass of xerogel pigment particles,which is typically then ground to a fine powder to provide porousxerogel pigment particles.

The terms “xerogel coating” and “xerogel coating layer,” as used herein,are synonymous with the term “xerogel layer”.

The term “binder,” as used herein, pertains to inorganic or organicmaterials which form a continuous structure or film in a substantiallycontinuous fashion from one outermost surface of a coating layer throughto the other outermost surface of the coating layer. As such, forexample, the xerogel, such as pseudo-boehmite or other metal oxidexerogel, of a xerogel layer is also a binder in addition to having axerogel structure with ultrafine pores.

A wide variety of materials known to form microporous xerogel layerswhen coated on a surface may be used to provide the microporous xerogellayers of the separator layers for the methods of the present invention.The electrical conductivity of the microporous separator layer of themethods of the present invention must be low enough to provide thenecessary insulating properties for the separator component when used inan electrochemical cell. Thus, for example, a highly electricallyconductive material, such as some vanadium oxides, that may formmicroporous xerogel layers when coated from a sol-gel liquid mixture ofa suitable precursor onto a surface may not be suitable in the methodsof preparing a cathode/separator assembly of this invention. Suitablematerials for use in the microporous xerogel layers of thecathode/separator assembly of the methods of the present inventioninclude, but are not limited to, pseudo-boehmites, zirconium oxides,titanium oxides, aluminum oxides, silicon oxides, and tin oxides.

In a preferred embodiment of the methods of preparing acathode/separator assembly of this invention, the separator layercomprises one or more microporous pseudo-boehmite layers. Microporouspseudo-boehmite layers for use as separators in electrochemical cellsare described in copending U.S. patent application Ser. Nos. 08/995,089and 09/215,112, both to Carlson et al. of the common assignee, thedisclosures of which are fully incorporated herein by reference. Theterm “pseudo-boehmite,” as used herein, pertains to hydrated aluminumoxides having the chemical formula Al₂O₃.xH₂O wherein x is in the rangeof from 1.0 to 1.5. Terms, as used herein, which are synonymous with“pseudo-boehmite,” include “boehmite,” “AlOOH,” and “hydrated alumina.”The materials referred to herein as “pseudo-boehmite” are distinct fromanhydrous aluminas (Al₂O₃, such as alpha-alumina and gamma-alumina), andhydrated aluminum oxides of the formula Al₂O₃.xH₂O wherein x is lessthan 1.0 or greater than 1.5.

The amount of the pores in a microporous layer may be characterized bythe pore volume, which is the volume in cubic centimeters of pores perunit weight of the layer. The pore volume may be measured by filling thepores with a liquid having a known density and then calculated by theincrease in weight of the layer with the liquid present divided by theknown density of the liquid and then dividing this quotient by theweight of the layer with no liquid present, according to the equation:

${{Pore}\mspace{14mu}{Volume}} = \frac{\left\lbrack {W_{1} - W_{2}} \right\rbrack/d}{W_{2}}$where W₁ is the weight of the layer when the pores are completely filledwith the liquid of known density, W₂ is the weight of the layer with noliquid present in the pores, and d is the density of the liquid used tofill the pores. Also, the pore volume may be estimated from the apparentdensity of the layer by subtracting the reciprocal of the theoreticaldensity of the materials (assuming no pores) comprising the microporouslayer from the reciprocal of the apparent density or measured density ofthe actual microporous layer, according to the equation:

${{Pore}\mspace{14mu}{Volume}} = \left( {\frac{1}{d_{1}} - \frac{1}{d_{2}}} \right)$where d, is the density of the layer which is determined from thequotient of the weight of the layer and the layer volume as determinedfrom the measurements of the dimensions of the layer, and d₂ is thecalculated density of the materials in the layer assuming no pores arepresent or, in other words, d₂ is the density of the solid part of thelayer as calculated from the densities and the relative amounts of thedifferent materials in the layer. The porosity or void volume of thelayer, expressed as percent by volume, can be determined according tothe equation:

${Porosity} = \frac{100\left( {{Pore}\mspace{14mu}{Volume}} \right)}{\left\lbrack {{{Pore}\mspace{14mu}{Volume}} + {1/d_{2}}} \right\rbrack}$where pore volume is as determined above, and d₂ is the calculateddensity of the solid part of the layer, as described above.

In one embodiment, the microporous xerogel layer of the microporousseparator layer of the methods of the present invention has a porevolume from 0.02 to 2.0 cm³/g. In a preferred embodiment, themicroporous xerogel layer has a pore volume from 0.3 to 1.0 cm³/g. In amore preferred embodiment, the microporous xerogel layer has a porevolume from 0.4 to 0.7 cm³/g. Below a pore volume of 0.02 cm³/g, thetransport of ionic species is inhibited by the reduced pore volume.Above a pore volume of 2.0 cm³/g, the amount of voids are greater whichreduces the mechanical strength of the microporous xerogel layer.

In contrast to conventional microporous separators which typically havepore diameters on the order of 0.03 to 2 microns, the microporousxerogel layers of the microporous separator layer of the methods of thepresent invention have pore diameters which range from about 0.3 micronsdown to less than 0.002 microns. In one embodiment, the microporousxerogel layer has an average pore diameter from 0.001 microns or 1 nm to0.3 microns or 300 nm. In a preferred embodiment, the microporousxerogel layer has an average pore diameter from 0.001 microns or 1 nm to0.030 microns or 30 nm. In a more preferred embodiment, the microporousxerogel layer has an average pore diameter from 0.003 microns or 3 nm to0.010 microns or 10 nm.

One distinct advantage of separators with much smaller pore diameters onthe order of 0.001 to 0.03 microns is that insoluble particles, evencolloidal particles with diameters on the order of 0.05 to 1.0 microns,can not pass through the separator because of the ultrafine pores. Incontrast, colloidal particles, such as conductive carbon powders oftenincorporated into cathode active layer compositions, may readily passthrough conventional separators, such as microporous polyolefins, andthereby may migrate to undesired areas of the cell.

Another significant advantage of the microporous separator layercomprising a microporous xerogel layer of the methods of the presentinvention, in comparison to conventional separators, is that thenanoporous structure of the xerogel layer may function as anultrafiltration membrane and, in addition to blocking all particles andinsoluble materials, may block or significantly inhibit the diffusion ofsoluble materials of relatively low molecular weights, such as 2,000 orhigher, while permitting the diffusion of soluble materials withmolecular weights below this cutoff level. This property may be utilizedto advantage in coating the cathode active layer and other layers ontothe surface of the separator layer by preventing any undesiredpenetration of pigments and other materials into the separator layer.This property may also be utilized to advantage in selectivelyimpregnating or imbibing materials into the separator layer duringmanufacture of the electrochemical cell or in selectively permittingdiffusion of very low molecular weight materials through the separatorlayer during all phases of the operation of the cell while blocking orsignificantly inhibiting the diffusion of insoluble materials or ofsoluble materials of medium and higher molecular weights.

Another important advantage of the extremely small pore diameters of themicroporous xerogel layer of the separator layer of the methods of thepresent invention is the strong capillary action of the tiny pores inthe xerogel layer which enhances the capability of the microporousseparators to readily take up or imbibe electrolyte liquids and toretain these materials in pores within the separator layer.

The microporous separator layers of the methods of this invention mayoptionally further comprise a variety of binders (in addition to thebinder, such as for example a pseudo-boehmite xerogel, that provides theprimary microporous structure of the separator layer), to improve themechanical strength and other properties of the layer, as for example,described for microporous pseudo-boehmite xerogel layers in the twoaforementioned copending U.S. patent application Ser. Nos. 08/995,089and 09/215,112, both to Carlson et al. of the common assignee. Anybinder that is compatible with the microporous material of the separatorlayer may be used. For microporous xerogel layers, any binder that iscompatible with the xerogel precursor sol during mixing and processinginto the microporous xerogel layer and provides the desired mechanicalstrength and uniformity of the layer without significantly interferingwith the desired microporosity is suitable for use. The preferred amountof binder is from 5% to 70% of the weight of the xerogel-formingmaterial in the layer. Below 5 weight percent, the amount of binder isusually too low to provide a significant increase in mechanicalstrength. Above 70 weight percent, the amount of binder is usually toohigh and fills the pores to an excessive extent, which may interferewith the microporous properties and with the transport of low molecularweight materials through the layer. The binder may be inorganic, forexample, another xerogel-forming material, such as silicas, gammaaluminum oxides, and alpha aluminum oxides, that are known to becompatible with the primary xerogel-forming material, such aspseudo-boehmite, present in the microporous layer, for example, as isknown in the art of ink-receptive microporous xerogel layers for ink jetprinting. In one embodiment, the binders in the microporous xerogellayer are organic polymer binders. Examples of suitable binders include,but are not limited to, polyvinyl alcohols, cellulosics, polyvinylbutyrals, urethanes, polyethylene oxides, copolymers thereof, andmixtures thereof. Binders may be water soluble polymers and may haveionically conductive properties. Suitable binders may also compriseplasticizer components such as, but not limited to, low molecular weightpolyols, polyalkylene glycols, and methyl ethers of polyalkylene glycolsto enhance the coating, drying, and flexibility of the microporousxerogel layer. These plasticizer components may be selected to alsoprovide useful properties as a component of the electrolyte.

The thickness of the microporous separator layer of the methods of thepresent invention may vary over a wide range since the basic propertiesof microporosity and mechanical integrity are present in layers of a fewmicrons in thickness as well as in layers with thicknesses of hundredsof microns. The microporous separator layer may be coated in a singlecoating application or in multiple coating applications to provide thedesired overall thickness. For various reasons, including cost, overallperformance properties of the microporous separator layer, and ease ofmanufacturing, the desirable overall thicknesses of the microporousseparator layer are in the range of 1 micron to 25 microns. Preferredare thicknesses in the range of 1 micron to 20 microns. More preferredare thicknesses in the range of 5 to 15 microns. Conventionalseparators, such as the porous polyolefin materials, are typically 25 to50 microns in thickness so it is particularly advantageous that themicroporous separator layers of this invention can be effective andinexpensive at thicknesses below 15 microns.

In the methods of preparing a cathode/separator assembly of the presentinvention, the temporary carrier substrate functions as a temporarysupport to the superposed layers during the process steps of thisinvention and may be any web or sheet material possessing suitablesmoothness, flexibility, dimensional stability, and adherence propertiesto the cathode/separator assembly. In one embodiment of the methods ofpreparing a cathode/separator assembly of the present invention, thetemporary carrier substrate is a flexible web substrate. Suitable websubstrates include, but are not limited to, papers, polymeric films, andmetals. A typical flexible polymeric film for use as the temporarycarrier substrate is a polyethylene terephthalate film. In a preferredembodiment, the flexible web substrate is surface treated with a releaseagent to enhance desired release characteristics, such as by treatmentwith a silicone release agent and the like. This surface treatment orcoating with a release agent of the temporary carrier substrate may bedone on a multistation coating machine in the same coating pass as thatused to later apply the first layer of the cathode/separator assembly inthe methods of this invention. Thus for example, referring to FIG. 1, inone embodiment of the methods of the present invention, the coating stepof coating the temporary carrier substrate with a release agent wouldoccur prior to the protective coating step 40. Examples of suitableflexible web substrates include, but are not limited to, resin-coatedpapers such as papers on which a polymer of an olefin containing 2 to 10carbon atoms, such as polyethylene, is coated or laminated; andtransparent or opaque polymeric films such as polyesters, polypropylene,polystyrene, polycarbonates, polyvinyl chloride, polyvinyl fluoride,polyacrylates, and cellulose acetate.

The temporary carrier substrate may be of a variety of thicknesses, suchas, for example, thicknesses in the range of 2 to 100 microns. Since thetemporary carrier substrate is subsequently removed from thecathode/separator assembly and is not present in the electrochemicalcell comprising the cathode/separator assembly, the temporary carriersubstrate may be thicker than the 2 to 3 micron thickness for anelectrochemically inactive substrate of the electrodes which is normallydesired to maximize the amount of electroactive materials in the cell.Thus, one benefit of the methods of this invention is the capability ofcoating the separator layer and the cathode active layer on a relativelythick substrate, such as a 12 to 25 micron thick polyethyleneterephthalate film, instead of being limited to a 2 or 3 micronsubstrate, or even a 6 micron substrate. Thinner substrates of 6 micronsor less are more difficult to coat and dry for mechanical handling anddimensional stability reasons, especially with relatively thickseparator layer and cathode active layer coatings which often are coatedfrom water or other high-boiling liquids.

Another benefit is that the temporary carrier substrate, after itsremoval from the cathode/separator assembly, may be reused for preparinganother cathode/separator assembly, may be reused for another productapplication, or may be reclaimed and recycled. Any such reuses combineto lower the effective cost of the temporary carrier substrate inpreparing the cathode/separator assembly.

In one embodiment of the methods of preparing a cathode/separatorassembly of this invention, the cathode active layer of the cathodecomprises an electroactive material selected from the group consistingof electroactive metal chalcogenides, electroactive conductive polymers,and electroactive sulfur-containing materials, and combinations thereof.As used herein, the term “chalcogenides” pertains to compounds thatcontain one or more of the elements of oxygen, sulfur, and selenium. Thecathode active layer of the cathode/separator assembly of the methods ofthe present invention may be coated in a single coating step, or,alternatively, the cathode active layer may be coated in multiplecoating steps to provide the desired overall thickness. The preparationof the cathode active layer may comprise other processing steps as knownin the art of cathode active coatings, such as, for example,calendering. The cathode active layer of the cathode/separator assemblyof the methods of the present invention may further comprise one or moreother non-electroactive components such as polymeric binders,electrically conductive materials, ionically conductive materials,non-electroactive metal oxides, and other additives known in the art ofcathode active layers.

The thickness of the cathode active layer may vary widely depending onthe type and thickness of the anode active layer and on the type andweight percent of the cathode active material in the cathode activelayer. Typical thicknesses are in the range of 5 to 200 microns with thecathode active layer more typically having a thickness of 10 to 30microns.

Examples of suitable transition metal chalcogenides include, but are notlimited to, the electroactive oxides, sulfides, and selenides oftransition metals selected from the group consisting of Mn, V, Cr, Ti,Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, andIr. Preferred transition metal chalcogenides are the electroactiveoxides of nickel, manganese, cobalt, and vanadium. In one embodiment,the cathode active layer comprises an electroactive conductive polymer.Examples of suitable conductive polymers include, but are not limitedto, electroactive and electronically conductive polymers selected fromthe group consisting of polypyrroles, polyanilines, polyphenylenes,polythiophenes, and polyacetylenes. Preferred conductive polymers arepolypyrroles, polyanilines, and polyacetylenes.

Preferred cathode active materials are those comprising electroactivesulfur-containing materials. The term “electroactive sulfur-containingmaterial,” as used herein, pertains to cathode active materials whichcomprise the element sulfur in any form, wherein the electrochemicalactivity involves the breaking or forming of sulfur—sulfur covalentbonds. The nature of the electroactive sulfur-containing materialsuseful in the cathode active layers of this invention may vary widely.The electroactive properties of elemental sulfur and of othersulfur-containing materials are known in the art, and typically includethe reversible formation of lithiated or lithium ion sulfides during thedischarge or cathode reduction cycle of the battery.

In one embodiment, the cathode active layer comprises elemental sulfur.

In one embodiment, the cathode active layer comprises an electroactivesulfur-containing material that is organic, that is, it comprises bothsulfur atoms and carbon atoms.

In one embodiment, the electroactive sulfur-containing material ispolymeric. In one embodiment, the cathode active layer comprises anelectroactive sulfur-containing organic polymer, wherein thesulfur-containing organic polymer, in its oxidized state, comprises oneor more polysulfide moieties, S_(m), selected from the group consistingof covalent —S_(m)— moieties, ionic —S_(m) ⁻ moieties, and ionic S_(m)²⁻ moieties, where m is an integer equal to or greater than 3 and is thesame or different at each occurrence, as, for example, described incopending U.S. Provisional Pat. Appl. Ser. Nos. 60/132,348 and60/132,393 to Movchan et al. and Kovalev et al., respectively, of thecommon assignee, the disclosures of which are fully incorporated hereinby reference. In a discharged state, an electroactive sulfur-containingorganic polymer is in an electrochemically reduced state and, whenpolysulfide moieties are present in the polymer, the polymer typicallyforms ionic organic polysulfides and sulfides along with some inorganicpolysulfides and sulfides during discharge. The microporous xerogellayers, such as pseudo-boehmite xerogel layers, may be beneficial incontrolling the concentration of these ionic species and their diffusionto the anode as, for example, described in copending U.S. patentapplication Ser. No. 08/995,089 to Carlson et al. of the commonassignee. In one embodiment, m of the polysulfide moiety, S_(m), of thesulfur-containing organic polymer is an integer equal to or greater than9 and is the same or different at each occurrence. In one embodiment, mof the polysulfide moiety, S_(m), of the sulfur-containing organicpolymer is an integer equal to or greater than 24 and is the same ordifferent at each occurrence. In one embodiment, the polysulfide moiety,S_(m), is covalently bonded by one or both of its terminal sulfur atomsas a side group on the polymer backbone chain of the sulfur-containingorganic polymer. In one embodiment, the polysulfide moiety, S_(m),comprises a covalent —S_(m)— moiety, which covalent —S_(m)— moiety isincorporated by covalent bonds to both of its terminal sulfur atoms intothe polymer backbone chain of the sulfur-containing organic polymer.

Examples of electroactive sulfur-containing organic polymers include,but are not limited to, those comprising one or more carbon-sulfurpolymers of general formulae (CS_(x))_(n) and (C₂S_(z)). Compositionscomprising the general formula —(CS_(x))_(n)— (formula I), wherein xranges from 1.2 to 2.3, and n is an integer equal to or greater than 2,are described in U.S. Pat. No. 5,441,831 to Okamoto et al. Additionalexamples include those wherein x ranges from greater than 2.3 to about50, and n is equal to or greater than 2, as described in U.S. Pat. Nos.5,601,947 and 5,690,702 to Skotheim et al. Additional examples ofelectroactive sulfur-containing polymers include those compositionscomprising the general formula —(C₂S_(z))_(n)— (formula II) wherein zranges from greater than 1 to about 100, and n is equal to or greaterthan 2, as described in U.S. Pat. Nos. 5,529,860 and 6,117,590 both toSkotheim et al. The preferred materials of general formulae I and II, intheir oxidized states, comprise a polysulfide moiety of the formula,—S_(m)—, wherein m is an integer equal to or greater than 3 and is thesame or different at each occurrence.

The backbone of electroactive sulfur-containing polymers may comprisepolysulfide —S_(m)— main chain linkages along with the presence ofcovalently bound —S_(m)— side groups. Owing to the presence of multiplelinked sulfur atoms, —S_(m)—, where m is an integer equal to or greaterthan 3, in these materials, they possess significantly higher energydensities than corresponding materials containing disulfide linkages,—S—S—, alone.

Other preferred electroactive sulfur-containing polymers are thosecomprising carbocyclic repeat groups, as described in copending U.S.patent application Ser. No. 08/995,122 to Gorkovenko et al. of thecommon assignee.

Other examples of electroactive sulfur-containing polymers comprising apolysulfide moiety, S_(m), where m is an integer that is equal to orgreater than 3, are one-dimensional electron conducting polymerscontaining at least one polysulfurated chain forming a charge transfercomplex with the polymer, as described in U.S. Pat. No. 4,664,991 toPerichaud et al.

Other examples of electroactive sulfur-containing polymers includeorgano-sulfur materials comprising disulfide linkages, although theirlow specific capacity compared to the corresponding materials containingpolysulfide linkages makes it difficult to achieve the desired highcapacities in electrochemical cells. However, they may also be utilizedin a blend in the cathode active layer with elemental sulfur and/or withsulfur-containing polymers comprising one or more polysulfide moietiesand may contribute by their electrochemical properties, their chemicalinteractions with lithium polysulfides and lithium sulfides generatedduring cycling of the cells, and, optionally, their melting propertiesduring fabrication of the cathode, to achieving the desired highcapacities in electrochemical cells. Examples of electroactivesulfur-containing materials comprising disulfide groups include thosedescribed in U.S. Pat. No. 4,739,018 to Armand et al.; U.S. Pat. Nos.4,833,048 and 4,917,974, both to DeJonghe et al.; U.S. Pat. Nos.5,162,175 and 5,516,598, both to Visco et al.; and U.S. Pat. No.5,324,599 to Oyama et al.

The relative amounts of electroactive cathode active material, such assulfur-containing organic polymer, and other components such asconductive additives, polymeric binders, electrolytes, and otheradditives in the cathode active layer may vary widely. Generally theserelative amounts are determined by experimentation and chosen so as tooptimize the amount of cathode active material present, the energystorage capacity of the cathode active layer, and the electrochemicalperformance of the cathode active layer in an electrochemical cell.

Electroactive sulfur-containing organic polymers for the cathode activelayers of the methods of the present invention typically have elementalcompositions containing between about 45 weight percent and 98 weightpercent of sulfur. In one embodiment, the sulfur-containing organicpolymer comprises greater than 75 weight percent of sulfur, and,preferably, greater than 86 weight percent of sulfur, and, mostpreferably, greater than 90 weight percent of sulfur.

Another embodiment of the methods of preparing a cathode/separatorassembly of the present invention is illustrated in FIG. 2. Referring toFIG. 2 (not drawn to scale), in a protective layer coating step 40, asecond protective coating layer 103 is coated onto the outer surface ofa first protective coating layer 101 of composite 14 comprisingprotective coating layer 101 and temporary carrier substrate 2, whichcomposite 14 may be prepared by the method illustrated in FIG. 1. Thisstep 40 forms composite 64 comprising temporary carrier substrate 2,first protective coating layer 101, and second protective coating layer103. Next, in a microporous separator coating step 50, a microporousseparator layer 102 is coated onto the surface of the second protectivecoating layer 103 to form composite 65 comprising temporary carriersubstrate 2, first protective coating layer 101, second protectivecoating layer 103, and microporous separator layer 102. Next, in acathode active layer coating step 60, a cathode active layer 201 iscoated in a desired pattern onto the surface of the microporousseparator layer 102 to form composite 66 comprising temporary carriersubstrate 2, first protective coating layer 101, second protectivecoating layer 103, microporous separator layer 102, and cathode activelayer 201. Following this step, in a temporary carrier substrateremoving step 70, the temporary carrier substrate 2 is removed from thefirst protective coating layer 101 of composite 66 to formcathode/separator assembly 67 comprising first protective coating layer101, second protective coating layer 103, microporous separator layer102, and cathode active layer 201.

In another embodiment of the methods of preparing a cathode/separatorassembly of the present invention, a first protective coating layer ofthe one or more protective coating layers of the cathode/separatorassembly is coated directly on the temporary carrier substrate, one ofthe one or more microporous layers of the separator layer is coateddirectly on this first protective coating layer, and a second protectivecoating layer of the one or more protective coating layers of thecathode/separator assembly is coated directly on this microporous layer,as illustrated in FIG. 3. Referring to FIG. 3 (not drawn to scale), in aprotective layer coating step 41, a second protective coating layer 103is coated onto the outer surface of the microporous separator layer 102of composite 15 comprising microporous separator layer 102, firstprotective coating layer 101, and temporary carrier substrate 2, whichcomposite 15 may be prepared by the method illustrated in FIG. 1. Thisstep 41 forms composite 18 comprising second protective coating layer103, microporous separator layer 102, first protective coating layer101, and temporary carrier substrate 2. Next, in a cathode active layercoating step 60, a cathode active layer 201 is coated in a desiredpattern onto the outer surface of the second protective coating layer103 to form composite 19 comprising cathode active layer 201, secondprotective coating layer 103, microporous separator layer 102, firstprotective coating layer 101, and temporary carrier substrate 2.Following this, in a temporary carrier substrate removing step 70, thetemporary carrier substrate 2 is removed from the first protectivecoating layer 101 of composite 19 to form cathode/separator assembly 20comprising cathode active layer 201, second protective coating layer103, microporous separator layer 102, and first protective coating layer101.

The second protective coating layers of the methods of the presentinvention may comprise the same materials and layers as described hereinfor the first protective coating layers of the methods of thisinvention. In one embodiment, the second protective coating layer is asingle ion conducting layer. In one embodiment, the second protectivecoating layer is an ionically conductive layer which is impervious todimethoxyethane and 1,3-dioxolane and combinations thereof.

In a preferred embodiment of the methods of preparing acathode/separator assembly of the present invention, the microporousseparator layer comprises one or more microporous pseudo-boehmitexerogel layers, and more preferably, the cathode/separator assemblyfurther comprises a second protective coating layer, wherein the secondprotective coating layer is in contact with at least one of the one ormore microporous pseudo-boehmite xerogel layers.

The incorporation of one or more protective coating layers in thecathode/separator assembly of the methods of this invention enhances themechanical strength and adds flexibility to microporous separator layerscomprising one or more microporous layers, particularly those separatorlayers comprising one or more microporous xerogel layers.

In one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, the desired pattern for coating thecathode active layer over the surface of the microporous separator layermay be full coverage of the cathode active layer over the surface of theseparator layer or, alternatively, the cathode active layer may notcompletely coat the surface of the separator layer. In one embodiment,the desired coating pattern of the cathode active layer completely coatsthe surface of the separator layer directly or indirectly, for example,as illustrated in FIG. 3, where cathode active layer 201 completelycoats the surface of protective coating layer 103 which in turncompletely coats the surface of microporous separator 102, thusproviding indirect complete coverage of the cathode active layer overthe surface of the separator layer. In one embodiment, the desiredcoating pattern of the cathode active layer does not completely coat thesurface of the separator layer directly or indirectly, for example, asillustrated in FIGS. 1, 2, 4 to 6, 7A, 7B, 8A, 8B, and 9 to 11. Thisabsence of full coverage of the cathode active layer directly over thesurface of the microporous separator layer or, alternatively, indirectlyover the surface of a protective coating layer over the microporousseparator layer may be beneficial to allow the coating of edgeinsulating layers in desired patterns on the separator layer and incontact with a portion of the cathode active layer to reduce thepossibility of short-circuiting of the electrodes when fabricated intoan electrochemical cell. This is also typically consistent with cuttingor slitting or otherwise converting the cathode/separator assembly, asoriginally coated, to a smaller size or dimension for fabrication intoan electrochemical cell, for example, as illustrated in FIGS. 4, 7A, 7B,8A, 8B, and 9 to 11.

In one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, the methods further comprise the stepof coating an edge insulating layer in a desired pattern on the surfaceof the microporous separator layer. In one embodiment, the step ofcoating the edge insulating layer occurs subsequent to the firstprotective layer, microporous separator, and the cathode active layercoating steps, and prior to the temporary carrier substrate removingstep, for example, as illustrated in FIG. 4. Referring to FIG. 4 (notdrawn to scale), in an edge insulating layer coating step 62, an edgeinsulating layer 301 is coated onto the outer surface of the microporousseparator layer 102 of composite 10 comprising cathode active layer 201,microporous separator layer 102, first protective coating layer 101, andtemporary carrier substrate 2, which composite 10 may be prepared by themethod illustrated in FIG. 1. This forms composite 24 comprising cathodeactive layer 201, edge insulating layer 301, microporous separator layer102, first protective coating layer 101, and temporary carrier substrate2. Next, in a temporary carrier substrate removing step 70, thetemporary carrier substrate 2 is removed from the first protectivecoating layer 101 of composite 24 to form cathode/separator assembly 25comprising cathode active layer 201, edge insulating layer 301,microporous separator layer 102, and first protective coating layer 101.If a smaller dimension is desired for the cathode/separator assembly 25,it may be slit or cut or otherwise converted to the desired smallerdimension in a slitting step 95 to form multiples of cathode/separatorassembly 31 comprising cathode active layer 201, edge insulating layer301, microporous separator layer 102, and first protective coating layer101.

In one embodiment, the desired pattern of the edge insulating layercomprises substantially the remaining area of the surface of themicroporous separator layer that is not coated with the desired patternof the cathode active layer, for example, as illustrated in FIG. 4.

In one embodiment, the step of coating the edge insulating layer occurssubsequent to the first protective layer and microporous separator layercoating steps, and prior to the cathode active layer coating step andthe temporary carrier substrate removing step, for example, asillustrated in FIG. 5. Referring to FIG. 5 (not drawn to scale), in anedge insulating layer coating step 62, an edge insulating layer 301 iscoated in a desired pattern onto the outer surface of the microporousseparator layer 102 of composite 15 comprising microporous separatorlayer 102, first protective coating layer 101, and temporary carriersubstrate 2, which composite 15 may be prepared by the methodillustrated in FIG. 1. This step 62 forms composite 26 comprising edgeinsulating layer 301, microporous separator layer 102, first protectivecoating layer 101, and temporary carrier substrate 2. Next, in a cathodeactive layer coating step 60, a cathode active layer 201 is coated in adesired pattern onto the surface of the microporous separator layer 102to form composite 24 comprising cathode active layer 201, edgeinsulating layer 301, microporous separator layer 102, first protectivecoating layer 101, and temporary carrier substrate 2. Following thisstep 60, in a temporary carrier substrate removing step 70, thetemporary carrier substrate 2 is removed from the microporous separatorlayer 102 of composite 24 to form cathode/separator assembly 25comprising cathode active layer 201, edge insulating layer 301,microporous separator layer 102, and first protective coating layer 101.

In one embodiment, a portion of the desired pattern of the edgeinsulating layer is in contact with a portion of the desired pattern ofthe cathode active layer, for example, as illustrated in FIGS. 4 and 5.

In one embodiment, the thickness of the edge insulating layer issubstantially the same as the thickness of the cathode active layer, forexample, as illustrated in FIGS. 4 and 5.

In one embodiment, the edge insulating layer comprises an insulatingxerogel layer such as, for example, a pseudo-boehmite xerogel layer. Inone embodiment, the insulating layer comprises an insulating non-porous,polymeric layer. Suitable insulating non-porous, polymeric layersinclude, but are not limited to, ethylene-propylene coating layers andisocyanate-crosslinked urethane coating layers. In one embodiment, theedge insulating layer is a single ion conducting layer. In oneembodiment, the edge insulating layer is an ionically conductive layerwhich is impervious to dimethoxyethane and 1,3-dioxolane andcombinations thereof.

In one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, the methods further comprise the stepof depositing a cathode current collector layer in a desired pattern onthe outer surface of the cathode active layer, for example, asillustrated in FIG. 6. In one embodiment, the step of depositing thecathode current collector layer occurs subsequent to the firstprotective layer, microporous separator, and cathode active layercoating steps, prior to the step of coating the edge insulating layer,and prior to the temporary carrier substrate removing step, for example,as illustrated in FIG. 6. Referring to FIG. 6 (not drawn to scale), in acathode current collector layer coating step 80, a cathode currentcollector layer 401 is coated in a desired pattern onto the cathodeactive layer 201 of composite 10 comprising cathode active layer 201,microporous separator layer 102, first protective coating layer 101, andtemporary carrier substrate 2, which composite 10 may be formed by themethod illustrated in FIG. 1. This step 80 forms composite 33 comprisingcathode current collector layer 401, cathode active layer 201,microporous separator layer 102, first protective coating layer 101, andtemporary carrier substrate 2. Next, in an edge insulating layer coatingstep 62, an edge insulating layer 301 in a desired pattern is coatedonto the microporous separator layer 102 to form composite 34 comprisingcathode current collector layer 401, cathode active layer 201, edgeinsulating layer 301, microporous separator layer 102, first protectivecoating layer 101, and temporary carrier substrate 2. Following this, ina temporary carrier substrate removing step 70, the temporary carriersubstrate 2 is removed from microporous separator layer 102 of composite34 to form cathode/separator assembly 36 comprising cathode currentcollector layer 401, cathode active layer 201, edge insulating layer301, microporous separator layer 102, and first protective coating layer101.

Suitable cathode current collector layers include, but are not limitedto, coating layers comprising conductive metal pigments, coating layerscomprising conductive carbons, coating layers comprising conductivegraphites, coating layers comprising conductive polymers, and coatinglayers comprising conductive metal oxide pigments. Other suitablecathode current collector layers include conductive metal layers suchas, for example, an aluminum layer, which may be coated or deposited bya vacuum deposition technique.

In one embodiment of the methods of preparing a cathode/separatorassembly of this invention, the methods further comprise a step ofdepositing a cathode current collector layer in a desired pattern on theouter surface of the cathode active layer and on the outer surface ofthe edge insulating layer, for example, as illustrated in FIGS. 7A and7B. In one embodiment, the step of depositing the cathode currentcollector layer occurs subsequent to the first protective layer,microporous separator, and cathode active layer coating steps,subsequent to the step of coating the edge insulating layer, and priorto the temporary carrier substrate removing step, for example, asillustrated in FIGS. 7A and 7B. Referring to FIG. 7A (not drawn toscale), in a cathode current collector layer coating step 80, a cathodecurrent collector layer 401 is coated in a desired pattern on thecathode active layer 201 and the edge insulating layer 301 of composite24, which composite 24 may be formed by the methods illustrated in FIGS.4 and 5. This step 80 forms composite 27 comprising cathode currentcollector layer 401, cathode active layer 201, edge insulating layer301, microporous separator layer 102, first protective coating layer101, and temporary carrier substrate 2. Next, in a temporary carriersubstrate removing step 70, the temporary carrier substrate 2 is removedfrom the microporous separator layer 102 of composite 27 to formcathode/separator assembly 28 comprising cathode current collector layer401, cathode active layer 201, edge insulating layer 301, microporousseparator layer 102, and first protective coating layer 101. If asmaller dimension is desired for cathode/separator assembly 28, in aslitting step 95, cathode/separator assembly 28 may be cut or slit toform multiples of cathode/separator assembly 32 comprising cathodecurrent collector layer 401, cathode active layer 201, edge insulatinglayer 301, microporous separator layer 102, and first protective coatinglayer 101. Referring to FIG. 7B (not drawn to scale), this is similar toFIG. 7A except that the sequence of the slitting step 95 and thetemporary carrier substrate removing step 70 are reversed. In both FIG.7A and FIG. 7B, the final product is cathode/separator assembly 32.

In one embodiment of the methods of preparing a cathode/separatorassembly of the present invention, the methods further comprise a stepof coating an electrode insulating layer in a desired pattern on theouter surface of the cathode current collector layer and on the surfaceof the edge insulating layer, for example, as illustrated in FIGS. 8Aand 8B. Referring to FIG. 8A (not drawn to scale), in an electrodeinsulating layer coating step 90, an electrode insulating coating layer501 is coated in a desired pattern onto the cathode current collectorlayer 401 and the edge insulating layer 301 of composite 23. This step90 forms composite 29 comprising electrode insulating layer 501, cathodecurrent collector layer 401, cathode active layer 201, edge insulatinglayer 301, microporous separator layer 102, first protective coatinglayer 101, and temporary carrier substrate 2. Next, in a temporarycarrier substrate removing step 70, the temporary carrier substrate 2 isremoved from the first protective coating layer 101 of composite 29 toform cathode/separator assembly 30 comprising electrode insulating layer501, cathode current collector layer 401, cathode active layer 201, edgeinsulating layer 301, microporous separator layer 102, and firstprotective coating layer 101. If a smaller dimension is desired forcathode/separator assembly 30, in a slitting step 95, cathode/separatorassembly 30 may be slit or cut to form multiples of cathode/separatorassembly 47 comprising electrode insulating layer 501, cathode currentcollector layer 401, cathode active layer 201, edge insulating layer301, microporous separator layer 102, and first protective coating layer101. FIG. 8B (not drawn to scale) is similar to FIG. 8A except that thesequence of the slitting step 95 and the temporary carrier substrateremoving step 70 are reversed. In both FIG. 8A and FIG. 8B, the finalproduct is cathode/separator assembly 47.

The terms “coating” and “depositing,” as used herein, are synonymous andpertain to the application of a layer of a material to another layer ofa material, such as to a substrate or to a coating layer on a substrate.

The various coating layers in the methods of preparing acathode/separator assembly of the present invention may be coated from aliquid mixture comprising a liquid carrier medium and the solidmaterials of the layer which are dissolved or dispersed in the liquidcarrier medium. The choice of the liquid carrier medium may vary widelyand includes water, organic solvents, and blends of water and organicsolvents. Exemplary organic solvents include, but are not limited to,alcohols, ketones, esters, and hydrocarbons. The choice of the liquidcarrier medium depends mainly on the compatibility with the particularsolid materials utilized in the specific coating layer, on the type ormethod of coating application to the receiving surface, and on therequirements for wettability and other coating application properties ofthe particular receiving surface for the coating. For example, forcoating a microporous xerogel layer, the liquid carrier medium istypically water or a blend of water with an alcohol solvent, such asisopropyl alcohol or ethyl alcohol, since the sol-gel materials that dryand condense to form the xerogel layer typically are most compatiblewith a water-based, highly polar liquid carrier medium.

The application of the liquid coating mixture to the temporary carriersubstrate or other layer may be done by any suitable process, such ascoating methods known in the art of coating liquid mixtures, forexample, wire-wound rod coating, spray coating, spin coating, reverseroll coating, gravure coating, slot extrusion coating, gap bladecoating, and dip coating. The liquid coating mixture may have anydesired solids content that is consistent with the viscosity andrheology that is acceptable in the coating application method. After theliquid coating mixture is applied on the temporary carrier substrate orother layer, the liquid carrier medium is typically removed to provide adried, solid coating layer. This removal of the liquid carrier mediummay be accomplished by any suitable process, such as methods of dryingcoatings known in the art, for example, hot air at a high velocity orexposure to ambient air conditions.

In an alternative approach, the coating layers of the present inventionmay be coated or deposited by vacuum deposition, sputtering, laserablation, or other non-liquid coating processes known in the art forapplying thin layers of metals, of inorganic materials, or of organicmaterials, and combinations thereof, to a substrate or to anothercoating layer.

Another aspect of the methods of preparing cathode/separator assembliesof the present invention pertains to laminating the cathode to thesurface of the microporous separator layer on the side opposite to thetemporary carrier substrate. One embodiment of this aspect of thisinvention is illustrated in FIG. 12. Referring to FIG. 12 (not drawn toscale), a laminating step 75 is used to combine composite 24 comprisinga temporary carrier substrate 2, a first protective coating layer 101, amicroporous separator layer 102, and an edge insulating layer 301 with acomposite 44 of a substrate 3, cathode current collector layer 4,cathode active layer 201, and a laminating layer 302 to form composite68 comprising temporary carrier substrate 2, first protective coatinglayer 101, microporous separator layer 102, edge insulating layer 301,cathode active layer 201, laminating layer 302, cathode currentcollector layer 4, and substrate 3. Substrate 3 may be a temporarycarrier substrate that is subsequently delaminated from cathode currentcollector layer 4, or substrate 3 may be permanently adhered to cathodecurrent collector layer 4. Next, in a temporary carrier substrateremoving step 70, the temporary carrier substrate 2 is removed from thefirst protective coating layer 101 of composite 68 to formcathode/separator assembly 72 comprising first protective coating layer101, microporous separator layer 102, edge insulating layer 301, cathodeactive layer 201, laminating layer 302, cathode current collector layer4, and substrate 3. If substrate 3 is also a temporary carriersubstrate, it can subsequently be removed.

Thus one aspect of the present invention pertains to methods ofpreparing a cathode/separator assembly of an electrochemical cell,wherein the cathode/separator assembly comprises a cathode comprising acathode active layer and a microporous separator layer, which methodscomprise the steps of (a) coating a first protective coating layer on atemporary carrier substrate, wherein the first protective coating layerhas a first surface in contact with the temporary carrier substrate andhas a second surface on the side opposite from the temporary carriersubstrate; (b) coating a microporous separator layer on the secondsurface of the first protective coating layer, wherein the separatorlayer has a first surface in contact with the second surface of thefirst protective coating layer and has a second surface on the sideopposite from the first protective coating layer; (c) laminating a firstsurface of the cathode in a desired adhesion pattern on the secondsurface of the separator layer; and (d) removing the temporary carriersubstrate from the first protective coating layer to form thecathode/separator assembly.

In one embodiment of preparing the cathode/separator assembly of thepresent invention, subsequent to step (b) and prior to step (c), themethod further comprises a step of coating an edge insulating layer in adesired pattern on the second surface of the separator layer, whereinthe edge insulating layer has a first surface in contact with the secondsurface of the separator layer and has a second surface on the sideopposite from the separator layer. In one embodiment of preparing thecathode/separator assembly of the present invention, the edge insulatinglayer is capable of being laminated to the first surface of the cathode.In one embodiment of preparing the cathode/separator assembly of thepresent invention, the edge insulating layer is coated on the secondsurface of the separator layer in the desired adhesion pattern for thelaminating of step (c). In one embodiment of preparing thecathode/separator assembly of the present invention, the edge insulatinglayer comprises an acrylic polymer. In one embodiment of preparing thecathode/separator assembly of the present invention, the edge insulatinglayer comprises a heat-expandable polymer layer comprising polymermicrocapsules containing a gas. In one embodiment of preparing thecathode/separator assembly of the present invention, the first surfaceof the cathode comprises a laminating layer in a desired adhesionpattern for the laminating of step (c). In one embodiment of preparingthe cathode/separator assembly of the present invention, the laminatinglayer comprises a heat-expandable polymer layer comprising polymermicrocapsules containing a gas. In one embodiment of preparing thecathode/separator assembly of the present invention, the edge insulatinglayer comprises an insulating non-porous, polymeric layer. In oneembodiment of preparing the cathode/separator assembly of the presentinvention, the edge insulating layer is an ionically conductive layerwhich is impervious to dimethoxyethane and 1,3-dioxolane, andcombinations thereof. In one embodiment of preparing thecathode/separator assembly of the present invention, the cathodecomprises a cathode current collector layer on a surface of the cathodeactive layer on the side opposite from the separator layer. In oneembodiment of preparing the cathode/separator assembly of the presentinvention, the cathode comprises an electrode insulating layer on asurface of the cathode current collector layer on the side opposite fromthe current collector layer. In one embodiment of preparing thecathode/separator assembly of the present invention, the cathodecomprises a temporary carrier substrate on the side opposite from theseparator layer in step (c). In one embodiment of preparing thecathode/separator assembly of the present invention, there is a furtherstep of removing the temporary carrier substrate from the cathode on theside opposite from the separator layer.

Cathode/Separator Assemblies

Another aspect of the present invention pertains to cathode/separatorassemblies prepared according to the methods of the present invention,as described herein. Thus, the cathode/separator assemblies of thepresent invention comprise a cathode active layer, a microporousseparator layer, and one or more protective coating layers, whichcathode/separator assemblies are prepared according to the methods ofthis invention.

Methods of Preparing Anode/Separator Assemblies

As described herein, the methods of preparing a microporous separatorlayer on a temporary carrier substrate for preparing cathode/separatorassemblies may usually be similarly applied to preparing anode/separatorassemblies by substituting the anode component for the relating cathodecomponent, such as, for example, substituting the anode active layer forthe cathode active layer. For example, referring to FIG. 3, if layer 201is an anode active layer instead of a cathode active layer as describedheretofore, the embodiment shown in FIG. 3 would form, in the case ofanode active layer 201, an anode/separator assembly 20 comprising anodeactive layer 201, second protective coating layer 103, microporousseparator layer 102, and first protective coating layer 101. In the caseof preparing an anode/separator assembly, second protective coatinglayer 103 is the key protective coating layer between the anode and theelectrolyte and the separator for improving the cycle life, safety, andother cell chemistry-related properties. In this case, the function ofthe first protective coating layer 101 is not primarily for protectionof the anode surface and may be primarily for better mechanicalproperties and/or better release properties from the temporary carriersubstrate. If protective coating layer 101 is deleted from FIG. 3, theprocess steps and the remaining layers correspond to Example 7.

Anode/Separator Assemblies

Another aspect of the present invention pertains to anode/separatorassemblies prepared according to the methods of the present invention,as described herein. Thus, the anode/separator assemblies of the presentinvention comprise an anode comprising an anode active layer and amicroporous separator layer, and optionally one or more protectivecoating layers interposed between the anode active layer and theseparator layer, which anode/separator assemblies are prepared accordingto the methods of this invention.

Methods of Preparing Electrochemical Cells

One aspect of the present invention pertains to methods of preparing anelectrochemical cell, which methods comprise the step of providing acathode/separator assembly prepared by the methods of this invention, asdescribed herein, or, alternatively, of providing an anode/separatorassembly prepared by the methods of this invention, as described herein.

In one embodiment, the present invention pertains to methods ofpreparing an electrochemical cell, which methods comprise the steps of:(a) providing a cathode/separator assembly prepared by a methodcomprising the steps of (i) coating a first protective coating layer, asdescribed herein, on a temporary carrier substrate, wherein the firstprotective coating layer has a first surface in contact with thetemporary carrier substrate and has a second surface on the sideopposite from the temporary carrier substrate; (ii) coating amicroporous separator layer on the second surface of the firstprotective coating layer, wherein the separator layer has a firstsurface in contact with the first protective coating layer and has asecond surface on the side opposite from the first protective coatinglayer; (iii) coating a cathode active layer in a desired pattern on thesecond surface of the separator layer, wherein the cathode active layerhas a first surface in contact with the second surface of the separatorlayer and has a second surface on the side opposite from the separatorlayer; and (iv) removing the temporary carrier substrate from the firstsurface of the first protective coating layer to form thecathode/separator assembly; (b) providing an anode; (c) providing acathode current collector layer; (d) providing an electrode insulatinglayer interposed between the anode and the cathode current collectorlayer; and (e) providing an electrolyte, wherein the electrolyte iscontained in the pores of the separator layer; and wherein the firstsurface of the first protective coating layer of the cathode/separatorassembly and the anode are positioned in a face-to-face relationship andthe second surface of the cathode active layer and the cathode currentcollector layer are positioned in a face-to-face relationship.

In one embodiment of the methods of preparing an electrochemical cell ofthis invention, the first protective coating layer is a single ionconducting layer, as described herein. Suitable single ion conductinglayers include, but are not limited to, glassy layers comprising aglassy material selected from the group consisting of lithium silicates,lithium borates, lithium aluminates, lithium phosphates, lithiumphosphorus oxynitrides, lithium silicosulfides, lithium germanosulfides,lithium lanthanum oxides, lithium titanium oxides, lithium borosulfides,lithium aluminosulfides, and lithium phosphosulfides. In a preferredembodiment, the single ion conducting layer comprises a lithiumphosphorus oxynitride. In one embodiment, the first protective coatinglayer is an ionically conductive layer which is impervious todimethoxyethane and 1,3-dioxolane and combinations thereof. In oneembodiment, the first protective coating layer comprises a polymerselected from the group consisting of electrically conductive polymers,ionically conductive polymers, sulfonated polymers, and hydrocarbonpolymers. In one embodiment, the first protective coating layercomprises an electrically conductive pigment. In one embodiment, thefirst protective coating layer comprises an aromatic hydrocarbon.

In one embodiment, the first protective coating layer comprises anionically conductive polymer. In a preferred embodiment, the ionicallyconductive polymer is a polydivinyl-poly(ethylene glycol). In oneembodiment, the first protective coating layer comprises a sulfonatedpolymer. In one embodiment, the sulfonated polymer is a sulfonatedpolystyrene.

In one embodiment, the first protective coating layer comprises amicroporous xerogel layer. Suitable materials for the microporousxerogel layer of the first protective coating layer include, but are notlimited to, oxides selected from the group consisting ofpseudo-boehmite, zirconium oxide, titanium oxide, aluminum oxide,silicon oxide, and tin oxide. In a preferred embodiment, the material ofthe xerogel layer comprises pseudo-boehmite or zirconium oxide, orcombinations thereof. In one embodiment, the microporous xerogel layercomprises an organic polymer. In one embodiment, the microporous xerogellayer of the first protective coating layer comprises an ionicallyconductive polymer in the pores of the microporous xerogel layer. In oneembodiment, the ionically conductive polymer in the pores of the xerogellayer is a polydivinylpoly(ethylene glycol). In one embodiment, theionically conductive polymer in the pores of the xerogel layer is asulfonated polymer.

In one embodiment, the first protective coating layer comprises arelease agent. In one embodiment, the release agent of the xerogel layercomprises a perfluorinated moiety.

In one embodiment, the microporous separator layer comprises one or moremicroporous xerogel layers. In one embodiment, the cathode/separatorassembly further comprises a second protective coating layer, whereinthe second protective coating layer is in contact with at least one ofthe one or more microporous layers of the separator layer.

In one embodiment of the methods of preparing an electrochemical cell ofthis invention, the cell is a secondary cell. In one embodiment of themethods of preparing an electrochemical cell of this invention, the cellis a primary cell. The methods of preparing an electrochemical cell ofthe present invention further are useful for preparing fuel cells,sensors, supercapacitors, electrochromic devices, and the like, in whichmicroporous separators or thin protective coatings are also part of theoverall product designs.

In a preferred embodiment of the methods of preparing an electrochemicalcell of this invention, the microporous separator layer comprises one ormore microporous pseudo-boehmite xerogel layers. In a more preferredembodiment, the cathode/separator assembly further comprises a secondprotective coating layer, wherein the second protective coating layer isin contact with at least one of the one or more microporouspseudo-boehmite layers.

Suitable electroactive materials in the cathode active layer for themethods of preparing an electric current producing cell of the presentinvention include, but are not limited to, electroactive transitionmetal chalcogenides, electroactive conductive polymers, andelectroactive sulfur-containing materials, as described herein.

A wide variety of anode active materials may be utilized in the anodesfor the methods of preparing an electrochemical cell of the presentinvention. Suitable anode active materials for the anodes include, butare not limited to, hydrogen-storing alloys for use withnickel-containing cathodes, and one or more metals or metal alloys or amixture of one or more metals and one or more alloys, wherein the metalsare selected from the Group IA and IIA metals in the Periodic Table.Examples of suitable anode active materials include, but are not limitedto, alkali-metal intercalated conductive polymers, such as lithium dopedpolyacetylenes, polyphenylenes, polypyrroles, and the like, andalkali-metal intercalated graphites and carbons. Anode active materialscomprising lithium are especially useful. Preferred anode activematerials in the methods of preparing an electrochemical cell of thisinvention are lithium metal, lithium-aluminum alloys, lithium-tinalloys, lithium-intercalated carbons, and lithium-intercalatedgraphites.

The electrolyte used in the present invention functions as a medium forstorage and transport of ions, and may be any of the types ofelectrolytes known in the art of electrochemical cells. Any liquid,solid, or solid-like material capable of storing and transporting ionsmay be used, so long as the material is sufficiently chemically andelectrochemically stable with respect to the anode and the cathode andthe material facilitates the transportation of ions between the anodeand the cathode without providing electrical conductivity that mightcause a short circuit between the anode and the cathode. Electrolytesmay be aqueous, non-aqueous, organic, or inorganic.

Examples of suitable electrolytes for use in the methods of preparing anelectrochemical cell of the present invention include, but are notlimited to, electrolytes comprising one or more electrolytes selectedfrom the group consisting of liquid electrolytes, gel polymerelectrolytes, solid polymer electrolytes, and single ion conductingelectrolytes. In a preferred embodiment, the electrolyte comprises aliquid electrolyte.

Examples of suitable liquid electrolytes include, but are not limitedto, those comprising one or more electrolyte solvents selected from thegroup consisting of water, N-methyl acetamide, acetonitrile, carbonates,sulfones, sulfolanes, aliphatic ethers, cyclic ethers, glymes,siloxanes, dioxolanes, N-alkyl pyrrolidones, substituted forms of theforegoing, and blends thereof, to which is added an appropriate ionicelectrolyte salt.

The electrolyte solvents of these liquid electrolytes are themselvesuseful as plasticizers in semi-solid or gel polymer electrolytes.Suitable gel polymer electrolytes include, but are not limited to, thosecomprising, in addition to one or more electrolyte solvents sufficientto provide the desired semi-solid or gel state, one or more polymers.Examples of suitable polymers include, but are not limited to, thoseselected from the group consisting of polyethylene oxides (PEO),polypropylene oxides, polyacrylonitriles, polysiloxanes,polyphosphazenes, polyimides, polyethers, sulfonated polyimides,polydivinyl polyethylene glycols, polyethylene glycol diacrylates,polyethylene glycol dimethacrylates, derivatives of the foregoing,copolymers of the foregoing, crosslinked and network structures of theforegoing, and blends of the foregoing; to which is added an appropriateionic electrolyte salt.

Solid polymer electrolytes useful in the present invention include, butare not limited to, those comprising one or more polymers selected fromthe group consisting of polyethers, polyethylene oxides (PEO),polypropylene oxides, polyimides, polyphosphazenes, polyacrylonitriles,polysiloxanes, polyether grafted polysiloxanes, derivatives of theforegoing, copolymers of the foregoing, crosslinked and networkstructures of the foregoing, and blends of the foregoing; to which isadded an appropriate ionic electrolyte salt. The solid polymerelectrolytes of this invention may optionally further comprise one ormore electrolyte solvents, typically at a level of less than 20 percentby weight of the solid polymer electrolyte.

To improve the ionic conductivity and other electrochemical properties,the electrolyte typically comprises one or more ionic electrolyte salts.As used herein, liquid electrolytes, gel polymer electrolytes, and solidpolymer electrolytes comprise an ionic electrolyte salt.

Examples of ionic electrolyte salts suitable for use in the presentinvention include, but are not limited to, MBr, MI, MClO₄, MAsF₆, MSCN,MSO₃CF₃, MSO₃CH₃, MBF₄, MB(Ph)₄, MPF₆, MC(SO₂CF₃)₃, MN(SO₂CF₃)₂,

and the like, where M is Li or Na. Other electrolyte salts useful in thepractice of this invention are alkali metal hydroxides, lithiumpolysulfides, lithium salts of organic ionic polysulfides, and thosedisclosed in U.S. Pat. No. 5,538,812 to Lee et al. Preferred ionicelectrolyte salts are LiI, LiSCN, LiSO₃CF₃ (lithium triflate), andLiN(SO₂CF₃)₂ (lithium imide).

In one embodiment of the methods of preparing an electrochemical cell ofthe present invention, the electrode insulating layer comprises apolymeric plastic film, such as, for example, a polyethyleneterephthalate film, a polyethylene naphthalate film, and a polyimidefilm. In one embodiment, the electrode insulating layer comprises apolymeric coating, such as, for example, an ethylene-propylene polymercoating.

Since the one or more microporous xerogel layers of the separator layerof the methods of this invention are usually impermeable to highmolecular weight materials such as the polymers typically used in gelpolymer electrolytes and solid polymer electrolytes, it is preferable tointroduce the polymer component of the electrolyte in a low molecularweight monomer or macromonomer form into the pores of the xerogel layer,such as in a coating step prior to the cathode active layer coating stepor in a coating step after the step of removing the temporary carriersubstrate from the separator layer. Subsequently, the low molecularweight monomer or macromonomer may be cured into a polymer to providethe desired type of solid polymer or gel polymer electrolyte. Suitablemonomers or macromonomers include, but are not limited to, heat- orradiation-curable monomers or macromonomers. Examples include, but arenot limited to, divinyl ethers such as tetraethylene glycol divinylether and urethane acrylate macromonomers. To provide sensitivity toultraviolet (UV) or visible radiation when the monomers or macromonomersdo not absorb significantly, a photosensitizer, as known in the art ofsensitization of photocurable coatings, may be added to acceleratecuring of the monomers or macromonomers into a polymeric material. Forexample, a small amount of a UV sensitizer, such as 0.2% by weight ofthe monomers or macromonomers, may be added. The typically transparentor nearly transparent nature of the microporous layers of the separatorlayer of the methods of this invention is beneficial in allowing thesensitizing ultraviolet or visible radiation to efficiently penetratethroughout the separator layer. Also, the positioning of the separatorlayer may be on the outside of the cell stack when the electrolyte ispresent in pores of the separator, for example, as illustrated for cellstack 38 in FIG. 9 and for cell stack 54 in FIG. 10. This isparticularly convenient for carrying out radiation curing of theelectrolyte with ultraviolet or visible radiation.

Another aspect of the present invention pertains to methods of preparingan electrochemical cell, which methods comprise the steps of (a)providing a cathode/separator assembly prepared by a method comprisingthe steps of (i) coating a first protective coating layer on a temporarycarrier substrate, wherein the first protective coating layer has afirst surface in contact with the temporary carrier substrate and has asecond surface on the side opposite from the temporary carriersubstrate; (ii) coating a microporous separator layer on the secondsurface of the first protective coating layer, wherein the separatorlayer has a first surface in contact with the first protective coatinglayer and has a second surface on the side opposite from the firstprotective coating layer; (iii) coating a cathode active layer in adesired pattern on the second surface of the separator layer, whereinthe cathode active layer has a first surface in contact with the secondsurface of the separator layer and has a second surface on the sideopposite from the separator layer; (iv) coating an edge insulating layerin a desired pattern on the second surface of the separator layer,wherein the edge insulating layer has a first surface in contact withthe second surface of the separator layer and has a second surface onthe side opposite from the separator layer; and (v) removing thetemporary carrier substrate from the first surface of the firstprotective coating layer to form the cathode/separator assembly; (b)providing an anode; (c) providing a cathode current collector layer; (d)providing an electrode insulating layer interposed between the anode andthe cathode current collector layer; and (e) providing an electrolyte,wherein the electrolyte is contained in the pores of the separatorlayer; wherein the first surface of the first protective coating layerof the cathode/separator assembly and the anode are positioned in aface-to-face relationship and the second surface of the cathode activelayer and the cathode current collector layer are positioned in aface-to-face relationship.

Another aspect of the present invention pertains to methods of preparingan electrochemical cell, which methods comprise the steps of (a) coatinga first protective coating layer on a temporary carrier substrate, asdescribed herein; (b) coating a microporous separator layer, asdescribed herein, on the first protective coating layer, (c) coating acathode active layer, as described herein, in a desired pattern on asurface of the separator layer, which surface is on the side of theseparator layer opposite from the first protective coating layer; (d)depositing a cathode current collector layer in a desired pattern on asurface of the cathode active layer, which surface is on the side of thecathode active layer opposite from the separator layer; (e) depositingan electrode insulating layer in a desired pattern on a surface of thecathode current collector layer, which surface is on the side of thecathode current collector layer opposite from the cathode active layer;(f) depositing an anode current collector layer in a desired pattern ona surface of the electrode insulating layer, which surface is on theside of the electrode insulating layer opposite from the cathode currentcollector layer; (g) depositing an anode active material layer in adesired pattern on a surface of the anode current collector layer, whichsurface is on the side of the anode current collector layer oppositefrom the electrode insulating layer; (h) removing the temporary carriersubstrate from the first protective coating layer; and (i) providing anelectrolyte, wherein the electrolyte is contained in the pores of theseparator layer. In one embodiment, step (g) of the methods furthercomprises depositing an anode protective coating layer on the anodeactive material. In one embodiment, the anode protective coating layeris a single ion conducting layer, as described herein for the protectivecoating layers in contact to the separator layer. Suitable single ionconducting layers for the anode protective coating layer include, butare not limited to, glassy layers comprising a glassy material selectedfrom the group consisting of lithium silicates, lithium borates, lithiumaluminates, lithium phosphates, lithium phosphorus oxynitrides, lithiumsilicosulfides, lithium germanosulfides, lithium lanthanum oxides,lithium titanium oxides, lithium borosulfides, lithium aluminosulfides,and lithium phosphosulfides. In a preferred embodiment, the single ionconducting layer comprises a lithium phosphorus oxynitride. In oneembodiment, the anode protective coating layer is an ionicallyconductive layer, as described herein, which is impervious todimethoxyethane and 1,3-dioxolane and combinations thereof. In oneembodiment, the anode protective coating layer comprises a polymer, asdescribed herein for the protective coating layers in contact with theseparator layer, which polymer is selected from the group consisting ofelectrically conductive polymers, ionically conductive polymers,sulfonated polymers, and hydrocarbon polymers. In one embodiment, theanode protective coating layer comprises an electrically conductivepigment, as described herein for the protective coating layers incontact with the separator layer. In one embodiment, the anodeprotective coating layer comprises an aromatic hydrocarbon, as describedherein for the protective coating layers in contact with the separatorlayer. In one embodiment, the anode protective coating layer comprises ametal, such as copper, that blends with, diffuses into, or forms analloy with lithium.

Another aspect of this invention pertains to methods of preparing anelectrochemical cell comprising a casing and a multilayer cell stack,which methods comprise the steps of (a) providing a laminar combinationof: (i) an anode assembly comprising an anode comprising an anode activelayer; wherein the anode active layer comprises an anode active materialcomprising lithium, a first cathode current collector layer, and anelectrode insulating layer interposed between the anode and the firstcathode current collector layer, and (ii) a cathode/separator assemblycomprising a first protective coating layer having a first surface and asecond surface on the side opposite to the first surface, a microporousseparator layer having a first surface in contact with the secondsurface of the first protective coating layer and having a secondsurface on the side opposite to the first protective coating layer, acathode active layer in a first desired coating pattern on the secondsurface of the microporous separator layer, and an edge insulating layerin a second desired coating pattern on the second surface of theseparator layer, wherein the cathode active layer has a first surface incontact in the first desired coating pattern with the second surface ofthe separator layer and has a second surface on the side opposite fromthe separator layer, and the edge insulating layer has a first surfacein contact in the second desired coating pattern with the second surfaceof the separator layer and has a second surface on the side opposite tothe separator layer; wherein the first cathode current collector layerand the second surface of the cathode active layer are positioned in aface-to-face relationship; (b) winding the laminar combination to forman anode-electrode insulating layer-first cathode current collectorlayer-cathode/separator assembly multilayer cell stack, wherein thefirst cathode current collector layer is in contact with the secondsurface of the cathode active layer; (c) providing an electrolyte,wherein the electrolyte is contained in the pores of the separator layerof the multilayer cell stack; (d) providing a casing to enclose themultilayer cell stack; and (e) sealing the casing. FIG. 9 illustratesone embodiment of this aspect of the methods of the present invention.

The term “multilayer cell stack,” as used herein, pertains to a cellstack, which cell stack within an electrochemical cell, when viewed in across-section of at least one profile plane, has more than oneelectrochemical layer, i.e., more than one combined anode-electrolyteelement-cathode construction. A single layer cell stack has only oneanode-electrolyte element-cathode construction when viewed in across-section of at least one profile plane. The term “casing,” as usedherein, pertains to the outermost surface of an electrochemical cell,where the outermost surface is adjacent to the multiple electrochemicalanode-electrolyte element-cathode layers or multilayer cell stack andacts as a seal or barrier against the transport of liquids or volatilematerials into or out of the cell stack.

A wide variety of barrier materials may be utilized for the casing inthe methods of preparing multilayer electrochemical cells of thisinvention. Suitable barrier materials include, but are not limited to,metal films, plastic-metal composite films, plastic films, and rigidmetal sheeting and cans. The basic requirement of the barrier materialsis that they can be sealed by a suitable process, such as heating,ultrasonic welding, or laser welding, to form a sealed casing for theelectrochemical cell, in which the barrier material in the sealed casingprovides a barrier against the leakage of fluids through the casing. Forexample, the barrier material may be provided as two sheets of matchedsize which are positioned on either side of the cell stack andsubsequently sealed on all four edges to form the casing of a prismaticcell.

Referring to FIG. 9 (not drawn to scale), in a combining step 100, acathode/separator assembly 31 comprising cathode active layer 201, edgeinsulating layer 301, microporous separator layer 102, and firstprotective coating layer 101, which cathode/separator assembly 31 may beformed by the method illustrated in FIG. 4, is combined with an anodeassembly 35 comprising an anode active layer 701, anode currentcollector layer 601, electrode insulating layer 501, and cathode currentcollector layer 401 to form an anode-electrode insulatinglayer-cathode/separator assembly combination 38. Next, in a winding step110, combination 38 is wound, stacked, or otherwise combined to form ananode-electrode insulating layer-cathode/separator assembly multilayercell stack 39. Following this step 110, in an electrolyte filling andsealing step 120, multilayer cell stack 39 is provided with electrolytein the pores of the separator and is further provided with a casing 200which is sealed around the cell stack to form electrochemical cell 210.The cell stack and the casing may be of a variety of shapes and sizesincluding, but not limited to, cylindrical and prismatic.

The term “prismatic,” as used herein, pertains to a solid shape where atleast two surfaces are substantially flat and parallel to each other.The dimensions of the cell stacks produced in the methods of the presentinvention depend on the widths and lengths of the anode andcathode/separator assemblies as wound, stacked, or otherwise combinedinto a multilayer cell stack and, optionally, on any slitting or cuttingof these assemblies that occurs after the winding step. Typically, theanode assembly and the cathode/separator assembly are of similar, butdistinct, widths and lengths and may be slightly offset from each otheron the edges to allow for more efficient electrical connections by tabsand other electrical contacts and for more effective insulation againstinternal short circuits, as known in the art of battery fabrication as,for example, described in U.S. Pat. No. 5,439,760 to Howard et al. andU.S. Pat. No. 5,549,717 to Takeuchi et al. Also, the anode assembly andthe cathode/separator assembly may be of identical widths or,alternatively, may be wound, stacked, or otherwise combined indimensions greater than the desired dimensions in the cell stack andsubsequently may be cut down to the desired dimensions.

Tabs are well known in the art of fabricating electrochemical cells,including cylindrical and prismatic cells, for providing the connectionsbetween the anode and the cathode to the external circuit for the cell.For example, in the methods of preparing electrochemical cells of thepresent invention, one or more tabs may be connected to the anode andthen attached or fed through the casing of the cell for connection tothe external circuit. For anodes comprising lithium metal, for examplelithium foil, the connection of the tab to the anode may be directly tothe lithium metal or, alternatively, may be to an anode currentcollector layer, if one is present in the anode. Suitable materials foruse in the anode tabs include, but are not limited to, nickel andcopper, such as, for example, 0.125 inch thick nickel tabs. These metaltabs to the anode may be attached to the lithium metal of the anode orto the anode current collector layer, if one is present, by a variety ofconventional methods, such as, for example, by applying pressure or byultrasonic welding.

For the cathodes of the methods of preparing electrochemical cells ofthe present invention, the connection of one or more tabs is typicallymade to the cathode current collector layer. Suitable materials for usein the cathode tabs include, but are not limited to, aluminum, nickel,silver, tin, and stainless steel. These metal tabs to the cathode may beattached to the cathode current collector layer by a variety of methodsknown in the art, such as, for example, by applying pressure or byultrasonic welding.

The insertion and attachment of the tabs to the anode and to the cathodemay occur at various steps in the methods of preparing electrochemicalcells of the present invention as long as it occurs before thecompletion of the filling step with the electrolyte. For example, thetabbing steps on the anode and the cathode may be done prior to thewinding step; or may be done subsequent to the winding step, but beforethe filling and sealing step.

The leads of the tabs protrude from the cell stack and, particularly inthe case of prismatic cells, may extend from the casing after sealing sothat the leads may be connected to the external circuit. These leads maybe part of the original tabs that were attached to the electrodes or maybe conductive extensions that have been attached or added to theoriginal tabs. To prevent any short circuits between the anode and thecathode, the one or more anode tabs and the one or more cathode tabs aremaintained in an electrically insulated relationship to each other.

As the layers in a multilayer cell stack of an electrochemical cellbecome thinner and the total surface areas of the anode and cathodebecome larger, it becomes progressively more difficult to achieveefficient collection of the current from the cell using a single tab, ora small number of tabs, from the anode and from the cathode to theexternal circuit. Also, current collection through only a few tabs or asingle tab to a lithium metal foil anode in a large surface area cell,such as, for example, 1000 cm² of lithium metal foil anode in aprismatic cell with external dimensions of 34 mm wide, 70 mm long, and 7mm thick, may have a shortened cycle life due to severing or loss oflithium metal at the tab connections. This would prevent currentcollection from any portion of the cell no longer connected electricallyto the severed tab connection. Accordingly, it is advantageous to do acontinuous edge contacting of the edges of the anode and the cathode inaddition to at least one tab to the anode and to the cathode to collectthe current from the continuous edge contacting for connection to theexternal circuit.

When the anode of the methods of preparing electrochemical cells of thepresent invention is lithium metal which also acts as the anode currentcollector layer, the edge of the lithium metal anode may be placed inelectrical contact by a variety of methods including, but not limitedto, ultrasonic welding and metal spraying. In one embodiment, the edgeof the lithium metal anode extends beyond the corresponding edges of thecathode active layer, the microporous separator layer, and the firstprotective coating layer, and substantially all of the lithium metalextensions are placed in electrical contact by ultrasonic welding.

When the anode of the methods of preparing electrochemical cells of thisinvention comprises an anode active layer comprising lithium and ananode current collector layer, as described herein, the edge of theconductive layer of the anode current collector layer may be placed inelectrical contact by a variety of methods including, but not limitedto, metal spraying. In one embodiment, the edge of the anode currentcollector layer provides a plurality of anode contact edges for themultilayer cell stack; and a metallic layer is deposited in electricalcontact with the anode current collector layers at substantially all ofthe anode contact edges. Suitable metals for the metallic layer include,but are not limited to, copper and nickel. Preferably, the metalliclayer is deposited by metal spraying. In one embodiment, the conductivematerial of the anode current collector layer comprises copper, and theelectrode insulating layer of the cell is selected from the groupconsisting of polymeric plastic films and polymeric coatings.

When the cathode of the methods of preparing electrochemical cells ofthe present invention comprises a cathode current collector layer, asdescribed herein, the edge of the cathode current collector layer may beplaced in electrical contact by a variety of methods including, but notlimited to, ultrasonic welding and metal spraying. In one embodiment,the edge of the cathode current collector layer provides a plurality ofcathode contact edges for the multilayer cell stack; and a metalliclayer is deposited in electrical contact with the cathode currentcollector layers at substantially all of the cathode contact edges; and,preferably, the edge of the cathode current collector layer extendsbeyond the corresponding edges of the cathode active layer, themicroporous separator layer, the first protective coating layer, and theanode. Suitable metals for the metallic layer include, but are notlimited to, aluminum, nickel, silver, tin, and stainless steel.Preferably, the metallic layer is deposited by metal spraying.

The electrolyte may be introduced into the cathode/separator assembly inpart or completely at various steps in the methods of preparing anelectrochemical cell of this invention. Typically, the electrolyte isintroduced into the cathode/separator assembly after the casing isformed around the cathode/separator/anode assembly through an opening inthe casing. This filling step is followed by the complete sealing of thecasing by closing the fill opening. Alternatively, the electrolyte maybe introduced before the casing is formed around thecathode/separator/anode assembly, as, for example, described in U.S.patent application Ser. No. 09/215,029 titled “Methods for PreparingPrismatic Cells,” filed Dec. 17, 1998, to Thibault et al. of the commonassignee, the disclosure of which is fully incorporated herein byreference. Also, part or all of the electrolyte may be impregnated intothe pores of the cathode/separator assembly 31 before the winding step110, as, for example, described in U.S. patent application Ser. No.08/995,089 to Carlson et al. of the common assignee.

In one embodiment of the methods of preparing an electrochemical cell ofthe present invention, a second cathode current collector layer isdeposited in a third desired pattern on the second surface of thecathode active layer and on the second surface of the edge insulatinglayer, for example, as illustrated in FIG. 10. Referring to FIG. 10 (notdrawn to scale), in a combining step 100, a cathode/separator assembly32 comprising second cathode current collector layer 401, cathode activelayer 201, edge insulating layer 301, microporous separator layer 102,and first protective coating layer 101, which cathode/separator assembly32 may be formed by the methods illustrated in FIGS. 7A and 7B, iscombined with an anode assembly 35 comprising anode active layer 701,anode current collector layer 601, electrode insulating layer 501, andfirst cathode current collector layer 402 to form an anode-electrodeinsulating layer-cathode/separator assembly combination 54. Next, in awinding step 110, combination 54 is wound, stacked, or otherwisecombined to form an anode-electrode insulating layer-cathode/separatorassembly multilayer cell stack 55. Following this step 110, in anelectrolyte filling and sealing step 120, multilayer cell stack 55 isprovided with electrolyte in the pores of the separator and is furtherprovided with a casing 200 which is sealed around the cell stack to formelectrochemical cell 210. The wide variety of sizes and shapes possiblefor the cell stack and the casing and the variety of options forintroducing the electrolyte at different steps in the process are asdescribed hereinabove for the embodiment illustrated in FIG. 9. In oneembodiment, as illustrated, for example, in FIG. 10, the anode furthercomprises an anode current collector layer interposed between the anodeactive layer and the electrode insulating layer.

In one embodiment of the methods of preparing an electrochemical cell ofthis invention, the cathode/separator assembly of step (a) furthercomprises a temporary carrier substrate on the first surface of theprotective coating layer, and the methods further comprise a step ofremoving the temporary carrier substrate from the first surface of thefirst protective coating layer prior to completion of step (b). In oneembodiment, a second cathode current collector layer in a third desiredcoating pattern is deposited on the second surface of the cathode activelayer and on the second surface of the edge insulating layer.

In one embodiment of the methods of preparing an electrochemical cell ofthe present invention, the anode of the anode assembly and the firstsurface of the protective coating layer of the cathode/separatorassembly are positioned in a face-to-face relationship in step (a), anda first cathode current collector layer-electrode insulatinglayer-anode-cathode/separator assembly multilayer cell stack is formedin step (b), wherein the anode is in contact with the first surface ofthe protective coating layer. In one embodiment, a second cathodecurrent collector layer is deposited in a third desired coating patternon the second surface of the cathode active layer and on the secondsurface of the edge insulating layer.

Another aspect of this invention pertains to methods of preparing anelectrochemical cell comprising a casing and a multilayer cell stack,which methods comprise the steps of (a) providing a laminar combinationof: (i) an anode assembly comprising an anode comprising lithium metal;and, (ii) a cathode/separator assembly comprising a first protectivecoating layer having a first surface and a second surface on the sideopposite to the first surface, a microporous separator layer having afirst surface in contact with the second surface of the first protectivecoating layer and a second surface on the side opposite from the firstprotective coating layer, a cathode active layer in a first desiredcoating pattern on the second surface of the microporous separatorlayer, and an edge insulating layer in a second desired coating patternon the second surface of the separator layer, wherein the cathode activelayer has a first surface in contact in the first desired coatingpattern with the second surface of the separator layer and has a secondsurface on the side opposite from the separator layer, and the edgeinsulating layer has a first surface in contact in the second desiredcoating pattern with the second surface of the separator layer and has asecond surface on the side opposite to the separator layer; a cathodecurrent collector layer in a third desired coating pattern on the secondsurface of the cathode active layer and on the second surface of theedge insulating layer, wherein the cathode current collector layer has afirst surface in contact with the second surface of the cathode activelayer and has a second surface on the side opposite from the cathodeactive layer; an electrode insulating layer in a fourth desired coatingpattern on the second surface of the cathode current collector layer andon the second surface of the edge insulating layer, wherein theelectrode insulating layer has a first surface in contact with thesecond surface of the cathode current collector layer and has a secondsurface on the side opposite from the cathode current collector layer;wherein the anode and the second surface of the electrode insulatinglayer are positioned in a face-to-face relationship: (b) winding thelaminar combination to form an anode-electrode insulating layer-cathodecurrent collector layer-cathode/separator assembly multilayer cellstack; (c) providing an electrolyte, wherein the electrolyte iscontained in the pores of the separator layer of the multilayer cellstack; (d) providing a casing to enclose the multilayer cell stack; and(e) sealing the casing.

FIG. 11 illustrates one embodiment of this aspect of the methods of thepresent invention.

Referring to FIG. 11 (not drawn to scale), in a combining step 100,cathode/separator assembly 47 comprising an electrode insulating layer501, cathode current collector layer 401, cathode active layer 201, edgeinsulating layer 301, microporous separator layer 102, and firstprotective coating layer 101, which assembly 47 may be formed by themethods illustrated in FIGS. 8A and 8B, is combined with an anodeassembly 42 comprising an anode active layer 701 comprising lithiummetal to form an cathode/separator assembly-anode assembly combination48. Next, in a winding step 110, combination 48 is wound, stacked, orotherwise combined to form an electrode insulatinglayer-cathode/separator assembly-anode assembly multilayer cell stack 49having alternating assemblies of cathode/separator assembly 47 and anodeassembly 42. Following this step 110, in an electrolyte filling andsealing step 120, multilayer cell stack 49 is provided with electrolytein the pores of the separator layer and is further provided with acasing 200 which is sealed around the cell stack to form theelectrochemical cell 210. The wide variety of sizes and shapes possiblefor the cell stack and the casing and the variety of options forintroducing the electrolyte at different steps in the process are asdescribed hereinabove for the embodiment illustrated in FIG. 9.

In one embodiment, the cathode/separator assembly of step (a) furthercomprises a temporary carrier substrate on the first surface of thefirst protective coating layer, and the methods further comprise thestep of removing the temporary carrier substrate from the first surfaceof the first protective coating layer prior to completion of step (b).In one embodiment, the anode and the first surface of the firstprotective coating layer of the cathode/separator assembly arepositioned in a face-to-face relationship in step (a), and ananode-cathode/separator assembly-cathode current collectorlayer-electrode insulating layer multilayer cell stack is formed in step(b).

A particular benefit of the methods of preparing electrochemical cellsof the present invention is that only two layers, an anode assembly anda cathode/separator assembly, need to be combined in a laminar mannerand then wound to form a multilayer cell stack instead of the morecomplex three layers of an anode assembly, a free-standing separator,and a cathode, in a typical cell fabrication method. Also, one aspect ofthe methods of preparing electrochemical cells of this inventionpertains to only a single layer of anode, electrolyte element, andcathode which may be coated or deposited on a single temporary carriersubstrate and then wound, after removing the temporary carriersubstrate, to form a multilayer cell stack. Also, as illustrated inFIGS. 9 to 11, the anode assembly may have layers which may all bedeposited by vacuum metalization or other metalizing techniques onto anelectrode insulating layer, such as, for example, a polyester film; andthe cathode/separator assembly may have layers which may all be coatedby liquid-based coating methods, as known in the art of coating methods,onto the temporary carrier substrate, which is subsequently removed.This has the advantage of potentially having each assembly, either anodeassembly or cathode/separator assembly, involve only a singlemanufacturing coating method so that each finished assembly mayconveniently be prepared on a single unit of production equipment andpossibly in a single processing pass through the equipment. A furtherbenefit is that the finished electrochemical cell contains only thesubstrate, if any, associated with the anode assembly. Thecathode/separator assembly in the electrochemical cell may have nosubstrate since the temporary carrier substrate is removed prior topreparing the electrochemical cell. This is very important forminimizing the volume and weight of electrochemically inactivesubstrates in order to maximize the volumetric and gravimetric energydensity of the electrochemical cell. For example, only 2 or 3 microns ofan electrochemically inactive substrate in a AA size cell having anelectrode area of 1000 cm² can result in a significant loss of energydensity. Also, as illustrated, for example, in FIG. 11 with a lithiummetal anode, the electrode insulating layer may be coated as a layer ofthe cathode/separator assembly and may be a very thin and tough coatingsuch that no substrate is present in the electrochemical cell.

Electrochemical Cells

Another aspect of the present invention pertains to electrochemicalcells prepared according to the methods of the present invention, asdescribed herein. Thus, in one embodiment, the electrochemical cells ofthe present invention comprise a cathode having a cathode active layer,an anode, and an electrolyte element interposed between the cathode andthe anode, wherein the electrolyte element comprises (a) a microporousseparator layer and (b) an electrolyte contained in pores of theseparator; wherein the cells comprise a cathode/separator assemblycomprising the cathode active layer, the microporous separator layer,and optionally one or more protective coating layers, whichcathode/separator assembly is prepared according to the methods of thepresent invention as described herein.

In another embodiment, the electrochemical cells of the presentinvention comprise an anode having an anode active layer, a cathode, andan electrolyte element interposed between the anode and the cathode,wherein the electrolyte element comprises (a) a microporous separatorlayer and (b) an electrolyte contained in pores of the separator;wherein the cells comprise a anode/separator assembly comprising theanode active layer, the microporous separator layer, and optionally oneor more protective coating layers, which anode/separator assembly isprepared according to the methods of the present invention as describedherein.

EXAMPLES

Several embodiments of the present invention are described in thefollowing examples, which are meant by way of illustration and not byway of limitation.

Example 1

A coating mixture for a first step of making a protective coating layerwas prepared by adding 17.5 g of a 4% by weight solution of polyvinylalcohol (AIRVOL 125, a trademark for polyvinyl alcohol polymersavailable from Air Products, Inc., Allentown, Pa.) in water to 10.0 g ofa 7.0% by weight solids solution of boehmite sol in water (CATALOIDAS-3, a trademark for aluminum boehmite sols available from Catalysts &Chemicals Ind. Co., Ltd., Tokyo, Japan) and stirring to mix thematerials. 0.10 g of ZONYL FSO-100, a trademark for non-ionicfluorochemical compounds available from E.I. duPont de Nemours,Wilmington, Del., was added with stirring to make the sol gel coatingmixture. Using a gap coating with a slot opening of a set thickness todoctor the coating, the sol gel coating mixture was applied to thenon-treated surface of 23 micron thick MELINEX 6328, a trademark forpolyethylene terephthalate (PET) films available from DuPont TeijinFilms, Wilmington, Del. After air drying in a laboratory hood under ahigh rate of circulation, a smooth and uniform microporous xerogel layerwith a dry thickness of 0.7 microns was formed on the PET plastic filmsubstrate. Using the dry coating density and thickness method describedherein, the porosity of this xerogel coating layer was calculated to be50%.

A coating mixture for the second step of making the protective coatinglayer was prepared by adding 0.3 g of a 2:1 molecular complex ofdimethoxyethane (DME or monoglyme):lithium tetrafluoroborate (LiBF₄) to10 g of poly(ethylene glycol) divinyl ether (average molecular weight ofabout 240; available from Aldrich Chemical Company, Milwaukee, Wis.) andstirring to mix the two liquid components. The molecular weight of thepoly(ethylene glycol) divinyl ether is about that of the divinyl etherof tetraethylene glycol. Using the same gap coating method with the slotopening, the multifunctional monomer coating mixture with the latentlithium ion catalyst was coated to fill the pores of the 0.7 micronxerogel layer and then cured at 130° C. for 2 minutes to crosslink themonomer to form the protective coating layer ofpolydivinyl-poly(ethylene glycol) in the pores of the boehmite xerogellayer. This protective coating layer was impervious to any penetrationby dimethoxyethane (DME), 1,3-dioxolane, or 50:50 blends by weight ofDME and 1,3-dioxolane when these liquids were placed on its surface.Also, this protective coating layer was impervious to penetration byDME, 1,3-dioxolane, or 50:50 DME:1,3-dioxolane containing 0.1 M lithiumoctasulfide when these liquids were placed on its surface. The etherstructure of the crosslinked polydivinyl-poly(ethylene glycol) and ofthe ethylene oxide groups of the ZONYL FSO-100, as well as the smallresidual amount of the latent lithium ion catalyst provided ionicconductivity in the thin protective coating layer.

A coating mixture for a microporous separator layer was prepared byadding 17.5 g of a 4% by weight solution of AIRVOL 125 polyvinyl alcoholin water to 10.0 g of a 7.0% by weight solids solution of CATALOID AS-3boehmite sol in water and stirring to mix the materials. 0.014 g ofZONYL FSO-100 was added with stirring to make the sol gel separatorcoating and to help promote good wetting of the separator coating on theprotective coating layer which contains a high level of ZONYL FSO-100.Using the same gap coating method with a slot opening, the sol gelseparator mixture was applied to the protective coating layer ofcrosslinked polydivinyl-poly(ethylene glycol) in the pores of theboehmite xerogel layer. After air drying in a laboratory hood under ahigh rate of air circulation, a smooth and unifrom microporous xerogellayer with a dry thickness of 7 microns was formed on the protectivecoating layer. A second microporous xerogel layer with a dry thicknessof 7 microns was similarly formed on the first xerogel separator layerto give a total dry thickness of 14 microns. The porosity of thisxerogel separator layer was calculated to be 50% from using the drycoating density and thickness method.

A cathode active layer with a composition by weight on a dry basis of70% elemental sulfur (available from Aldrich Chemical Company,Milwaukee, Wis.), 20% PRINTEX XE-2 conductive carbon (a trademark forcarbon pigments available from Degussa Corporation, Akron, Ohio), 5%FLUKA graphite 50870 (a trademark for graphite available from FlukaChemical Company, Ronkonkoma, N.Y.), and 5% of LUVISKOL VASSE polyvinylpyrrolidone-vinyl acetate (PVP/VA) copolymer (a trademark for polymersavailable from BASF Corporation, Mount Olive, N.J.) was prepared bysuspending the dry ingredients in isopropanol and stirring, followed byadding the 50% solution of PVPNA to provide an overall coating mixsolids of 14% and then grinding in a ball mill for 12 hours. The cathodeactive layer coating mix was then coated onto the microporous xerogelseparator layer using a second gap coating with slot opening thatprovided a narrower coating width than for the separator layer. Afterair drying as done for the separator coating, a uniform cathode activecoating layer with a dry thickness of 15 microns was formed on theseparator layer. There were uncoated lanes of separator layer on bothsides of the cathode active layer due to the different widths of thecoating applications.

The resulting composite of PET film as the temporary carrier substrate,the protective coating layer, the microporous separator layer, and thecathode active layer could be easily delaminated to cause thedelamination of the protective coating layer from the PET film, therebyremoving the PET film from the composite to form a free standingcathode/separator assembly of the protective coating layer, themicroporous separator layer, and the cathode active layer.

This free standing cathode/separator assembly was found to be suitablefor use in combining with an anode such as 50 micron lithium foil, anorganic liquid electrolyte such as a 1.4 M solution of lithium imide(available from 3M Corporation, St. Paul, Minn.) in a 42:58 volume ratiomixture of 1,3-dioxolane and dimethoxyethane, and a cathode currentcollector such as nickel foil, to prepare a rechargeable electrochemicalcell. The cell had a layered structure of anode-cathode/separatorassembly (with the protective coating layer in a face to facerelationship with the lithium anode)-cathode current collector with theliquid electrolyte filling the void areas of the microporous separatorand the cathode active layer. The cell showed an initial specificcapacity of over 500 mAh/g based on the weight of elemental sulfurpresent and showed more than a 20% increase in cycle life to a cutoff ofspecific capacity of 400 mAh/g, in comparison to a cell prepared in thesame manner, except without the protective coating layer. Also, thefree-standing cathode/separator assembly with the protective layer onone surface showed greatly increased mechanical strength and flexibilitywithout breaking, in comparison to a free-standing cathode/separatorassembly made in the same manner, except without the protective coatinglayer.

Example 2

A free-standing cathode/separator assembly was prepared as described inExample 1, except that a 5% solution of styrene-4-sulfonic acid sodiumsalt (available from Aldrich Chemical Company, Milwaukee, Wis.) wassubstituted for the multifunctional monomer coating mixture with thelatent lithium ion catalyst. This free-standing cathode/separatorassembly of Example 2 gave similar results when fabricated intorechargeable electrochemical cells as those found with thecathode/separator assembly of Example 1.

Example 3

A free-standing cathode/separator assembly was prepared as described inExample 1, except that a 7.0% by weight solids solution of ammoniumzirconyl carbonate prepared by adding water to BACOTE 20, a trademarkfor zirconium compounds available from Magnesium Eleckton, Flemington,N.J., was substituted for the CATALOID AS-3 in both the first step ofmaking the protective coating layer and in the step of making themicroporous xerogel separator layer. The ammonium zirconyl carbonate isa precursor to zirconium oxide sols and, upon coating and drying,provides a zirconium oxide xerogel layer. This free-standingcathode/separator assembly of Example 3 showed more than twice themechancial strength and flexibility without cracking as found with thefree-standing cathode/separator assembly of Example 1. The free-standingcathode/separator assembly of Example 3 gave similar results whenfabricated into rechargeable electrochemical cells as those found withthe cathode/separator assembly of Example 1.

Example 4

A free-standing cathode/separator assembly was prepared as described inExample 3, except that a 5% solution of styrene-4-sulfonic acid sodiumsalt (available from Aldrich Chemical Company, Milwaukee, Wis.) wassubstituted for the multifunctional monomer coating mixture with thelatent lithium ion catalyst. This free-standing cathode/separatorassembly of Example 4 gave similar results when tested for mechanicalstrength and flexibility and when fabricated into rechargeableelectrochemical cells as those found with the cathode/separator assemblyof Example 3.

Example 5

A free-standing cathode/separator assembly was prepared as described inExample 1, except that a coating mixture of 15% by weight solidssolution of PARALOID B-48 (a trademark for acrylic polymers availablefrom Rohm & Haas Corporation, Philadelphia, Pa.) in toluene was used toapply an edge insulating layer onto the uncoated lanes on the separatorlayer prior to the delaminating step. The dry thickness of the edgeinsulating layer of the insulating non-porous acrylic polymer layer wasthe same thickness as that of the cathode active layer. The edge of theacrylic edge insulating layer on one side was in contact to the edge ofone side of the cathode active layer. Special care was taken to coat theedge insulating layer only onto the separator layer and not to have anyof the edge insulating layer be coated onto the PET film where itsadhesion would interfere with the delamination step. Thus, the edgeinsulating layer was coated on the entire surface of the separator layerthat was not coated with the cathode active layer, but was not coatedonto the PET film. This free-standing cathode/separator assembly ofExample 5 gave similar results when fabricated into rechargeableelectrochemical cells as those found with the cathode/separator assemblyof Example 1.

Example 6

A free-standing cathode/separator assembly was prepared as described inExample 1, except that 0.10 g of FLUORAD FC-430 (a trademark forfluorochemical compounds available from 3M Corporation, St. Paul, Minn.)was substituted for the 0.10 g of ZONYL FSO-100 in the first step ofmaking the protective coating layer, and 0.014 g of FLUORAD FC-430 wassubstituted for the 0.014 g of ZONYL FSO-100 in the step of making themicroporous xerogel separator layer. This free-standingcathode/separator assembly of Example 6 gave similar results whenfabricated into rechargeable electrochemical cells as those found withthe cathode/separator assembly of Example 1. Both FLUORAD FC-430 andZONYL FSO-100 are perfluorinated compounds in that they both compriseperfluorinated moieties where the carbon atoms are fully substitutedwith fluorine instead of with hydrogen or other atoms, such as in CF₃—and —CF₂— moieties. The amount of Fluorad FC-430 used in the first stepof making the protective coating layer could be greatly increased by,for example, factors of 5 and 10, without significant loss of thexerogel character of the protective coating layer and withoutsignificant loss of mechanical strength and flexibility to theprotective coating layer. Increasing the amount of the FLUORAD FC-430 bya factor of 5 reduced the porosity to about 40%, and increasing theFLUORAD FC-430 by a factor of 10 reduced the porosity to about 10%.Progressively filling the pores of the xerogel layer with increasedamounts of a fluorochemical release agent, which is typically trapped byvirtue of its molecular weight in the pores, provides another approachfor a single step preparation of a first protective coating layerproviding a transport barrier against electrolyte solvents, anions ofthe ionic electrolyte salt, and anions of the cathode reduction productsfor increased cycle life of the electrochemical cell.

In contrast to the results with FLUORD FC-430, similarly increasing theamount of ZONYL FSO-100 in the first step of making the protectivecoating layer of Example 1 by a factor of 3 and of 5 significantlyreduced the mechanical strength of the protective coating layer and madeit very difficult to prepare the cathode/separator assembly. Also,replacing the 0.10 g of ZONYL FSO-100 in the first step of making theprotective coating layer with 0.10 g of either ZONYL FSN-100 or ZONYLFS-300 significantly reduced the mechanical strength of the protectivecoating layer and made it very difficult to prepare thecathode/separator assembly.

Example 7

A microporous separator layer was prepared as described in Example 1,except that no protective coating layer was coated first and the coatingmixture for the microporous separator layer was coated in two coatingapplications directly on the non-treated surface of the 23 micron thickMELINEX 6328 PET film to give a total dry thickness of 14 microns forthe xerogel separator layer. Using the dry coating density and thicknessmethod described herein, the porosity of this xerogel separator layerwas calculated to be 50%.

A coating mixture for making a protective coating layer was prepared byadding 0.3 g of the 2:1 molecular complex of dimethoxyethane (DME ormonoglyme):lithium tetrafluoroborate (LiBF₄) to 10 g of poly(ethyleneglycol) divinyl ether (available from Aldrich Chemical Company,Milwaukee, Wis.) and stirring to mix the two liquid components, asdescribed in Example 1. Using the gap coating method with the slotopening, the multifunctional monomer coating mixture with the latentlithium ion catalyst was applied in an amount equivalent to fill thepores of about 1 micron of the xerogel separator layer and immediatelycured at 130° C. for 2 minutes to crosslink the monomer to form theprotective coating layer of polydivinyl-poly(ethylene glycol) in thepores of the top surface of the boehmite xerogel separator layer. Thisprotective coating layer was impervious to any penetration bydimethoxyethane (DME), 1,3-dioxolane, or 50:50 blends by weight of DMEand 1,3-dioxolane when these liquids were placed on its surface. Also,this protective coating layer was impervious to penetration by DME,1,3-dioxolane, or 50:50 DME:1,3-dioxolane containing 0.1 M lithiumoctasulfide when these liquids were placed onits surface. The etherstructure of the crosslinked polydivinyl-poly(ethylene glycol), as wellas the small residual amount of the DME:LiBF₄ catalyst, provided ionicconductivity in the thin protective coating layer.

A lithium anode active layer was then deposited by vacuum depositiononto the protective coating layer using an ALAMO vacuum coater (atradname for vacuum coaters from Sierra Technology Group, Inc.,Livermore, Calif.) and a mask to give a narrower coating width than thecoating width of the protective coating layer. A uniform lithium layerwith a dry thickness of 8 microns was formed on the protective coatinglayer. There were uncoated lanes of protective coating layer on bothsides of the lithium layer due to the different widths of the coatingapplications.

The resulting composite of PET film as the temporary carrier substrate,the microporous separator layer, the protective coating layer, and thelithium anode active layer could be easily delaminated to cause thedelamination of the microporous separator layer from the PET film,thereby removing the PET film from the composite to form a free standinganode/separator assembly of the microporous separator layer, theprotective coating layer, and the anode active layer.

This free standing anode/separator assembly was found to be suitable foruse in combining with a cathode such as a 15 micron thick coating of acathode active layer containing 70% elemental sulfur, 20% PRINTEX XE-2,5% FLUKA graphite 50870, and 5% of LUVISKOL VA55E polyvinylpyrrolidone-vinyl acetate (PVP/VA) copolymer coated on one side of a 18micron thick conductive carbon coated aluminum foil (Product No. 60303available from Rexam Graphics, South Hadley, Mass.) as a currentcollector and substrate; an organic liquid electrolyte such as a 1.4 Msolution of lithium imide (available from 3M Corporation, St. Paul,Minn.) in a 42:58 volume ratio mixture of 1,3-dioxolane anddimethoxyethane; and an anode current collector such as nickel foil, toprepare a rechargeable electrochemical cell. The cell had a layeredstructure of cathode-anode/separator assembly (with the protectivecoating layer in contact to one side of the lithium anode)-anode currentcollector (in contact to the other side of the lithium anode) with theliquid electrolyte filling the void areas of the microporous separatorand the cathode. The cell showed an initial specific capacity of over400 mAh/g based on the weight of elemental sulfur present and showedmore than a 20% increase in cycle life to a cutoff of specific capacityof 320 mAh/g, in comparison to a cell prepared in the same manner,except without the protective coating layer. Also, the free-standinganode/separator assembly with the protective layer on one surface showedgreatly increased mechanical strength and flexibility without breaking,in comparison to a free-standing anode/separator assembly made in thesame manner, except without the protective coating layer.

Example 8

A free-standing anode/separator assembly was prepared as described inExample 7, except that a 5% solution of styrene-4-sulfonic acid sodiumsalt (available from Aldrich Chemical Company, Milwaukee, Wis.) wassubstituted for the multifunctional monomer coating mixture with thelatent lithium ion catalyst. This free-standing cathode/separatorassembly of Example 8 gave similar results when fabricated intorechargeable electrochemical cells as those found with thecathode/separator assembly of Example 7.

Example 9

A free-standing anode/separator assembly was prepared as described inExample 7, except that a 7.0% by weight solids solution of ammoniumzirconyl carbonate prepared by adding water to BACOTE 20, wassubstituted for the CATALOID AS-3 in the step of making the microporousxerogel separator layer. The ammonium zirconyl carbonate is a precursorto zirconium oxide sols and, upon coating and drying, provides azirconium oxide xerogel layer. This free-standing anode/separatorassembly of Example 9 showed more than twice the mechancial strength andflexibility without cracking as found with the free-standingcathode/separator assembly of Example 7. The free-standinganode/separator assembly of Example 9 gave similar results whenfabricated into rechargeable electrochemical cells as those found withthe cathode/separator assembly of Example 7.

Example 10

A 14 micron thick xerogel separator coating overcoated on a 0.7 micronprotective coating layer that had been coated in a two-step process onthe non-treated surface of 23 micron thick MELINEX 6328 PET film wasprepared as described in Example 1 and then cut to a 50 mm width in onedirection. Instead of then coating a cathode active layer over thexerogel separator coating, the cathode active layer was coated on 18micron thick carbon-coated aluminum foil (Product No. 60303, availablefrom Rexam Graphics, South Hadley, Mass.) using the cathode active layerformulation and coating procedure as described in Example 1 and cut to a45 mm width in one direction. An laminating layer was applied at a 3micron dry thickness and in a 4 mm wide strip to the surface on bothedges of the cathode active layer using a solution of FOAMCOAT (atrademark for heat-expandable coatings comprising a polymer microcapsulecontaining a gas, such as isobutene; available from Pierce & StevensCo., Buffalo, N.Y.).

The composite of the 14 micron thick xerogel separator coating/0.7micron thick protective coating layer/PET film was combined with thecomposite of the 15 micron thick cathode active layer with laminatingstrips on both edges/carbon-coated aluminum foil so that the xerogellayer was in contact to the cathode active layer and the separatorcomposite was evenly about 2.5 mm extended from each edge of the cathodecomposite. The two combined composites were held under pressure in aclamp and then heated for 1 minute at 130° C. to cause the laminatinglayer to adhere to the separator along with the expansion of theFOAMCOAT coating under those thermal conditions. The two combinedcomposites were strongly laminated together in the desired adhesionpattern corresponding to the coating pattern of the lamination layer ofFOAMCOAT in contact with the xerogel separator layer. The laminatedcomposites could then be readily delaminated from the temporary carriersubstrate to form a cathode/separator assembly comprising the protectivecoating layer, the microporous xerogel layer, and the cathode activelayer with the laminating layer on its two edges and adhered strongly tothe xerogel layer to provide an assembly that could be readily combined,by winding, stacking, or other processes, with an anode and othercomponents to fabricate an electrochemical cell.

The coating of the FOAMCOAT laminating layer on the cathode active layerhad a further benefit of impregnating some of the FOAMCOAT material intothe cathode active layer and of forming a mechanically strong, flexible,and elastomeric composite with the cathode active layer upon the thermalexpansion of the FOAMCOAT at 130° C. This greatly improved themechanical integrity of the cathode/separator assembly during thedelamination, cell fabrication, and cell discharge-charge cycling steps,especially to provide some mechanical strength and elastomericproperties to counter the stresses of expansion and contraction of thecell and its layers during cycling. In contrast, the cathode activelayer typically has such a high loading of electroactive materials andsuch a low loading of binders that the cathode active layer hasrelatively weak cohesive and mechanical strength and is easily damaged.

A laminating layer of FOAMCOAT could also be applied to the surface ofthe microporous xerogel layer since the microcapsules are much too largeto impregnate into the xerogel layer and also provided a strong adhesionby lamination upon combining under clamp pressure to the cathodecomposite and heating at 130° C. for 1 minute, both with and without acorresponding laminating layer of FOAMCOAT on the cathode active layer.

PARALOID B-48 acrylic resin was also effective as a laminating layer oneither or both the cathode active layer and the xerogel separator layerwhen substituted for the FOAMCOAT, but did not show the greatly enhancedmechanical, flexibility, and elastomeric properties when coated as anedge layer on the cathode active layer as were observed with FOAMCOAT.

These examples, and the descriptions of the present invention herein,provide a wide variety of options to utilize a microporous xerogel layercoated directly or indirectly on a temporary carrier substrate to becoated or laminated to form a cathode/separator assembly or ananode/separator assembly, which can then be subsequently coated orlaminated to form additional combined layers of an electrochemical cellincluding all the anode, cathode, and electrolyte layers needed for anelectrochemical cell. The use of a temporary carrier substrate as thesubstrate for the anode to be combined with a cathode/separator assemblyand, alternatively, the use of a temporary carrier substrate as thesubstrate for the cathode to be combined with an anode/separatorassembly provide useful options to remove unwanted substrates from beingfabricated as part of the finished electrochemical cell. Similarly, ithas been shown that the separator assembly, such as a xerogel separatorassembly, on a temporary carrier substrate may itself be used tolaminate to either a cathode or an anode.

While the invention has been described in detail and with reference tospecific and general embodiments thereof, it will be apparent to oneskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope thereof.

1. A method of preparing a cathode/separator assembly of anelectrochemical cell, wherein said cathode/separator assembly comprisesa cathode comprising a cathode active layer and a microporous separatorlayer, said method comprising the steps of: (a) coating a firstprotective coating layer on a temporary carrier substrate, wherein saidfirst protective coating layer has a first surface in contact with saidtemporary carrier substrate and has a second surface on the sideopposite from said temporary carrier substrate; (b) coating amicroporous separator layer on said second surface of said firstprotective coating layer, wherein said separator layer has a firstsurface in contact with said second surface of said first protectivecoating layer and has a second surface on the side opposite from saidfirst protective coating layer; (c) laminating a first surface of saidcathode in a desired adhesion pattern on said second surface of saidseparator layer; and (d) removing said temporary carrier substrate fromsaid first surface of said first protective coating layer to form saidcathode/separator assembly.
 2. The method of claim 1, wherein said firstprotective coating layer is a single ion conducting layer.
 3. The methodof claim 2, wherein the single ion conducting layer comprises a glassymaterial selected from the group consisting of lithium silicates,lithium borates, lithium aluminates, lithium phosphates, lithiumphosphorus oxynitrides, lithium silicosulfides, lithium germanosulfides,lithium lanthanum oxides, lithium titanium oxides, lithium borosulfides,lithium aluminosulfides, and lithium phosphosulfides, and combinationsthereof.
 4. The method of claim 3, wherein the single ion-conductinglayer further comprises a polymer.
 5. The method of claim 1, whereinsaid first protective coating layer is an ionically conductive layerwhich is impervious to dimethoxyethane and 1,3-dioxolane, andcombinations thereof.
 6. The method of claim 1, wherein said firstprotective coating layer comprises a polymer selected from the groupconsisting of electrically conductive polymers, ionically conductivepolymers, sulfonated polymers, and hydrocarbon polymers.
 7. The methodof claim 1, wherein said first protective coating layer comprises anionically conductive polymer.
 8. The method of claim 7, wherein saidionically conductive polymer is a polydivrnyl poly(ethylene glycol). 9.The method of claim 1, wherein said first protective coating layercomprises a sulfonated polymer.
 10. The method of claim 9, wherein saidsulfonated polymer is a sulfonated polystyrene.
 11. The method of claim1, wherein said first protective coating layer comprises a microporousxerogel layer.
 12. The method of claim 11, wherein said microporousxerogel layer comprises an organic polymer.
 13. A method of preparing anelectrochemical cell, said method comprising the steps of: (a) providinga cathode/separator assembly prepared by a method comprising the stepsof: (i) coating a first protective coating layer on a temporary carriersubstrate, wherein said first protective coating layer has a firstsurface in contact with said temporary carrier substrate and has asecond surface on the side opposite from said temporary carriersubstrate; (ii) coating a microporous separator layer on said secondsurface of said first protective coating layer, wherein said separatorlayer has a first surface in contact with said second surface of saidfirst protective coating layer and has a second surface on the sideopposite from said first protective coating layer; (iii) laminating afirst surface of a cathode in a desired adhesion pattern on said secondsurface of said separator layer, wherein said cathode comprises acathode active layer; and (iv) removing said temporary carrier substratefrom said first surface of said first protective coating layer to formsaid cathode/separator assembly; (b) providing an anode; and (c)providing an electrolyte, wherein said electrolyte is contained in thepores of said separator layer, wherein said first surface of said firstprotective coating layer of said cathode/separator assembly and saidanode are positioned in a face-to-face relationship.
 14. The method ofclaim 13, wherein said first protective coating is a single ionconducting layer.
 15. The method of claim 14, wherein the single ionconducting layer comprises a glassy material selected from the groupconsisting of lithium silicates, lithium borates, lithium aluminates,lithium phosphates, lithium phosphorus oxynitrides, lithiumsilicosulfides, lithium germanosulfides, lithium lanthanum oxides,lithium titanium oxides, lithium borosulfides, lithium aluminosulfides,and lithium phosphosulfides, and combinations thereof.
 16. The method ofclaim 14, wherein the single ion-conducting layer further comprises apolymer.
 17. The method of claim 13, wherein said first protectivecoating layer is an ionically conductive layer which is impervious todimethoxyethane and 1,3-dioxolane, and combinations thereof.
 18. Themethod of claim 13, wherein said first protective coating layercomprises a polymer selected from the group consisting of electricallyconductive polymers, ionically conductive polymers, sulfonated polymers,and hydrocarbon polymers.
 19. The method of claim 13, wherein said firstprotective coating layer comprises an ionically conductive polymer. 20.The method of claim 19, wherein said ionically conductive polymer is apolydivinyl-poly(ethylene glycol).
 21. The method of claim 13, whereinsaid first protective coating layer comprises a sulfonated polymer. 22.The method of claim 21, wherein said sulfonated polymer is a sulfonatedpolystyrene.
 23. The method of claim 13, wherein said first protectivecoating layer comprises a microporous xerogel layer.
 24. The method ofclaim 23, wherein said microporous xerogel layer comprises an organicpolymer.